'Trinity' is a theological term (derived from two Latin words, tres, three, and unitas, one); it is employed to express certain truths about God clearly taught in the Bible. The core truths that form this foundational Christian doctrine are these: (1) the unity of God; (2) the Father is God, the Son is God and the Holy Spirit is God; (3) the Father, the Son and the Holy Spirit are distinct persons.
Our belief in one God is fundamental; Christianity is a monotheistic religion. The Old and New Testaments both assert the unity of God: 'Hear, O Israel: The LORD our God, the LORD is one!' (Deut 6:4); 'I am the First and I am the Last; besides Me there is no God' (Isa 44:6); 'There is one God, and there is no other but He' (Mark 12:32).
Pagans believe in many gods. Even Satan is considered as 'the god of this world'. But Christians do not acknowledge pagan gods because they take the first commandment seriously: 'You shall have no other gods before me' (Ex 20:3). Christians deny polytheism (belief in many gods) because 'all the gods of the peoples are idols' – false gods (Ps 96:5). The apostle Paul writes: 'For all the gods of the peoples are idols' (1 Cor 8:5, 6).
God is often called Father. 'Blessed be the God and Father of our Lord Jesus Christ' (Eph 1:3). God is not Father because of his created sons (the angels), or because of his adopted sons (his redeemed children); rather, he is Father because of the eternal relation with his only-begotten Son. God is Father from eternity, from before the creation of the world, because he was ever with the Son. The Lord Jesus prayed to him: 'And now, O Father, glorify Me together with Yourself, with the glory which I had with You before the world was' (John 17:5). Since he cannot be Father without the Son, whoever denies that the Son is eternal is also denying the Father.
The Bible teaches explicitly that the Son is God and is equal with the Father. Like the apostle Thomas, every Christian looks to Jesus Christ and confesses: 'My Lord and my God!' (John 20:28). Christ is God because he has the attributes of God, is called by divine titles, and does things that only God is able to do.
The Son is eternal; he was with the Father before the creation (John 17:5). As man Jesus had a beginning, when he was conceived in Mary's womb; but he already existed as God before he came into this world. The prophet proclaimed that 'Whose goings forth are from of old, from everlasting' (Micah 5:2). Jesus is omnipotent, 'I am the Alpha and the Omega, the Beginning and the End ... who is and who was and who is to come, the Almighty' (Rev 1:8). He openly said he had the same power as the Father: 'whatever [the Father] does, the Son also does in like manner' (John 5:15-19). Since he can accomplish all things as the Father does, he must be omnipotent like him. He is omniscient. The apostles prayed: 'You, O Lord, who know the hearts of all' (Who except God knows the human heart?); and earlier they simply confessed: 'Now we are sure that You know all things' (see Acts 1:24; 1 Kings 8:39; John 16:30). The Lord Jesus is omnipresent and thus could promise his disciples that he will be with them even though physically he ascended back into heaven: 'And lo, I am with you always, even to the end of the age' (Matt 28:20). The existence of so many Christian assemblies all around the world are a witness of his omnipresence: 'For where two or three are gathered together in My name, I am there in the midst of them' (Matt 18:20). The Lord Jesus is also immutable, that is, he doesn't change. 'You are the same ... Jesus Christ is the same yesterday, today, and forever' (Heb 1:12; 13:8).
In the New Testament, Jesus is repeatedly called the Lord. Now we know that there are many masters, many lords; but we also know that there is only one Lord over all lords, only one Lord of the Sabbath, only one Lord of all people (Rev 19:16; Matt 12:8; Acts 10:36). The same title, Lord (Kurios), identifies Jesus with Yahweh, the name by which God was known among the children of Israel (compare Isa 40:3 with Matt 3:3; and Joel 2:32 with Rom 10:13). Furthermore, the Bible calls him specifically God. The angel announced that the son of Mary was to be called Emmanuel, which means 'God with us'. John opens his gospel with a simple yet profound declaration: 'The Word was God.' The apostle Thomas addresses him: 'My Lord and my God.' The apostle Paul writes that Christ 'the eternally blessed God' and, 'our great God and Savior'. The apostle Peter calls him, 'our God and Savior'. Finally, God the Father himself addressed the Son: 'Your throne, O God, is forever and ever' (Matt 1:21-23; John 1:1; 20:28; Rom 9:5; Titus 2:13; 2 Pet 1:1; Heb 1:8; cf. Ps 10:16; 45:6, 7).
The Lord Jesus performs such work as only God can perform. The Bibles teaches that the universe was created by Christ, the Word of God: 'All things were made through Him, and without Him nothing was made that was made.' 'You, LORD, in the beginning laid the foundation of the earth, and the heavens are the work of Your hands' (John 1:1, 3; Heb 1:8-10). Jesus is presently caring for his own creation: 'upholding all things by the word of His power (Heb 1:3). Even greater than the work of creation is the salvation of man. Scripture declares that Jesus Christ is the Savior of the world; he is the Savior of the body (the church); he is our Lord and Savior (see John 4:42; Eph 5:23; 2 Pet 1:11). Who but God can be the Saviour? At the consummation of the world, the Lord Jesus will judge all people since he 'was ordained by God to be Judge of the living and the dead' (Acts 10:42), and 'we must all appear before the judgment seat of Christ' (2 Cor 5:10). Who except God is competent to judge all mankind infallibly?
So, Scripture teaches that the Lord Jesus is eternal, omnipotent, omniscient, omnipresent and immutable. His name is Yahweh, God and Lord. Creation is his work; he is the Saviour and Judge of the world. The biblical evidence points to one irrefutable conclusion: Jesus Christ is God in the same sense as the Father is God, 'the brightness of His glory and the express image of His person' (Heb 1:3). It is with good reason that the angels and the redeemed ascribe to Christ the worship and adoration that is due to God alone (Rev 5:12-15).
God and Man
The Son is eternally God; in time he also became man when he was conceived in the womb of the virgin Mary. Since then he continues to be both God and man forever (see Isa 9:6, 7 and Jer 33:14-16). In the beginning of the gospel, John describes Christ as 'the Word' and declares that the Word was God. He proceeds by announcing that 'the Word became flesh and dwelt among us' (John 1:1, 14). Jesus is fully God and fully human, or, in the words of the apostle Paul, 'In Him dwells all the fullness of the Godhead bodily' (Col 2:9).
Before coming into the world, the Son was eternally with the Father in glory. In order to fulfill the plan of redemption, the Son humbled himself, became man, lived under the law, died and was buried. 'The Son of Man did not come to be served, but to serve, and to give His life a ransom for many' (Mark 10:45). After experiencing this state of humiliation, God the Father glorified him by raising him from the dead, exalted him above the heavens. Jesus is presently reigning on the Father's right hand, worshipped by all the redeemed (see Phil 2:5-11).
It was necessary that the Redeemer become man. We need a man like us to act as our representative before the Father, and who was able to suffer and die as a sacrifice for our sins. It was necessary that our Saviour be God because no-one else could save us from sin: 'I, even I, am the LORD, and besides Me there is no savior' (Isa 43:11).
The Scripture presents the Holy Spirit as a Divine Person. He is given the names and attributes of God himself; he also performs works as only God can perform. Besides, Scripture also shows that he is a person, not a mere force: he speaks, grieves, loves, chooses, sends and teaches, such activities as only a person can perform.
The Holy Spirit is a person
This does not imply that he has a physical body like ours. In this context, a 'person' is equivalent to 'someone' (rather than 'something') who is self-conscious -- who thinks, speaks, loves, feels and makes willing choices. Thus human beings and angels are persons because they are endowed with these personal qualities, whereas a mere 'force' or 'energy' is not personal. Angels are persons, even though they are spirit beings without a material body. They are persons because they think, speak and so forth. Similarly God is spirit; he does not have flesh and bones as we have. Nevertheless God is a person because he thinks, speaks, plans and loves. The same applies to the Holy Spirit. He does not have a physical form, but it is evident from Scripture that he is not simply a force since he manifests all the personal attributes.
The Spirit is powerful, but not simply 'a power'. Just as the Bible mentions the power of God (Matt 22:29), it also speaks of the power of the Holy Spirit (Rom 15:13). Power is one of his qualities.
The Spirit is intelligent: he knows and seeks the things of God (1 Cor 2:10, 11); he has a mind (Rom 8:27); he is able to teach men (1 Cor 2:13). He also has a will, and gives different gifts to the redeemed according to his good pleasure (1 Cor 12:11). He guides Christians in their activities (Acts 16:6-11). Like any other person, the Holy Spirit has emotions (he feels). The Bible therefore warns us not to grieve the Spirit of God (Eph 4:30).
The Holy Spirit performs personal actions. He leads us into the truth. He speaks (John 16:13), convicts (John 16:8), performs miracles (Acts 8:39), and intercedes for believers (Rom 8:26). A mere force cannot hear, speak or pray. Human beings also relate personally to the Holy Spirit. Christians hear and obey him (as did Peter, Acts 10:19-21), but sometimes they lie to him (Acts 5:3). Others put him to shame and even blaspheme the Spirit (Heb 10:29; Matt 12:31).
The Lord Jesus shows us that the Spirit is a person because he calls him 'another counsellor' like himself. 'And I will pray the Father, and He will give you another Helper, that He may abide with you forever' (John 14:16). Just as Jesus is a person, even so is the Spirit whom he has sent to take his residence in the church.
The Spirit is God
Once the Spirit is recognized as a person, it is relatively easy to recognize that he is a divine person. The Holy Spirit is God. He is called the Spirit of God and the Spirit of the Lord, and God calls him 'my Spirit'.
The Spirit has all the divine attributes: he knows all things (1 Cor 2:12); he is omnipresent (Ps 139:7); and he is eternal (Heb 9:14). He performs such work as only God is able to do. For instance, he creates (Gen 1:2; Job 33:4) and gives life (John 6:63).
The apostles were convinced that the Holy Spirit is God. What is done to the Spirit is done to God. For instance, the Apostle Peter warns one of the disciples: 'Ananias, why has Satan filled your heart to lie to the Holy Spirit ... You have not lied to men but to God' (Acts 5:3, 4).
The words of the Lord in the Old Testament are quoted in the New Testament as the words of the Spirit. For example, in the book of Isaiah, the Lord commands: 'Go, and tell this people: 'Keep on hearing, but do not understand; Keep on seeing, but do not perceive'' The apostle Paul quotes these words and says, 'The Holy Spirit spoke rightly through Isaiah the prophet to our fathers' (Isa 6:9; Acts 28:25). So the words of the Lord God are the words of the Holy Spirit. Similarly, what 'says the LORD' is actually the Holy Spirit speaking (compare Jer 31:31-34 with Heb 10:15).
If the Spirit is not God, than God does not truly dwell in our hearts. But we, Christians, are the temple of God because the Holy Spirit dwells in us. 'Do you not know that you are the temple of God and that the Spirit of God dwells in you ... do you not know that your body is the temple of the Holy Spirit who is in you?' (1 Cor 3:16; 6:19). Thus we confess that the Spirit is God, the Lord and Giver of life. Unbelievers deny the deity of the Holy Spirit, indeed they do not know him (John 14:17);
Scripture teaches that the Father, the Son and the Holy Spirit are distinct persons. The Father is neither the Son nor the Holy Spirit.
The Father sent his Son; the Son came to do the Father's will. Evidently, then, they are not one and the same person. In the same way the Holy Spirit is not the Father. Jesus said: 'The Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you' (John 14:26). Observe the three persons of the Trinity: the Father sends the Holy Spirit, and the Holy Spirit teaches us about the Son. The distinction between the three persons is evident.
Though the truths that form the doctrine of the Trinity are not difficult to grasp separately, it is extremely difficult to understand how the three Persons are one God. During the early centuries of the Christian era, the church endeavoured to give a correct definition of the relationship between the three Persons while maintaining the unity of God. This was done amidst a proliferation of heretical ideas:
1. Arianism is the denial of the deity of Christ. Early in the fourth century, a presbyter named Arius taught that the Son was a created being. Arius was opposed by Athanasius who proved from Scripture that Jesus is eternal, uncreated and fully God. The Council of Nicea (325 AD) affirmed the deity of Christ, stating that the Son is 'of the same substance' (homoousious) with the Father.
2. Modalism is the idea that God is one person who revealed himself at different times as the Father, the Son, and the Holy Spirit. Modalism 'confounds the persons', comparing God to an actor who assumes different roles at different times. However the Bible teaches that the three Persons co-exist at the same time. For instance, at his baptism, when Jesus came out of the water, the Holy Spirit descended upon him, and the voice of the Father was heard from heaven.
3. Tritheism is the idea that there are three separate gods who are united only insofar as they have a common purpose. Tritheism contradicts the monotheistic ('one God') doctrine of the Bible, which is expressed accurately in the Athanasian Creed: 'We worship one God in trinity, and trinity in unity. Neither confounding the persons (as modalism does), nor separating the substance (as tritheism does). For the person of the Father is one, of the Son another, and of the Holy Spirit another. But of the Father, of the Son, and of the Holy Spirit there is one divinity, equal glory and co-eternal majesty.'
There is no correct analogy of the Trinity. 'To whom then will you liken God? Or what likeness will you compare to Him?' (Isa 40:18). If we compare the Trinity to anything, we end up with a false picture of the true God. Christians do not believe in the Trinity because we are able to fully understand the being of God, but because we are convinced that the Bible teaches the unity of God, the deity of the three Persons, and their distinction from each other.
The Trinity and Salvation
Knowing God as a trinity of persons is closely connected with our experience of salvation. As Christians we believe that we are 'elect according to the foreknowledge of God the Father, in sanctification of the Spirit, for obedience and sprinkling of the blood of Jesus Christ' (1 Pet 1:2). For that reason we are baptised 'in the name of the Father and of the Son and of the Holy Spirit' (Matt 28:19). We are not baptised in three names, but in the one name of God. At the same time we acknowledge that this one God is the Father, the Son and the Holy Spirit. We worship one God, and experience blessings from each of the three persons: 'The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Spirit' (2 Cor 13:14).
How can anyone invoke the name of Jesus for salvation if he does not believe that he is truly God? God declares that he alone is Saviour. 'I, even I, am the LORD, and besides Me there is no savior' (Isa 43:11). How can anyone who sees Jesus as a mere creature claim to know God since the Bible teaches that the glory of God is known only in the face of Christ? 'You know neither Me nor My Father,' Jesus told the Jews who had rejected him, 'If you had known Me, you would have known My Father also' (John 8:19). It is to be expected that the same people who deny the Son would also deny also the Holy Spirit because, as Jesus himself said, 'the world cannot receive [the Spirit], because it neither sees Him nor knows Him' (John 14:17).
We cannot conclude that everyone who has an intellectual knowledge of the Trinity is really a believer. On the other hand, a true child of God is known by the worship and love he expresses towards God the Father, by his trust in the Lord Jesus Christ, and by the righteousness and holiness wrought in him by the Holy Spirit.