The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth. JOHN 1:14
Trinity and Incarnation belong together. The doctrine of the Trinity declares that the man Jesus is truly divine; that of the Incarnation declares that the divine Jesus is truly human. Together they proclaim the full reality of the Savior whom the New Testament sets forth, the Son who came from the Father’s side at the Father’s will to become the sinner’s substitute on the cross (Matt. 20:28; 26:36-46; John 1:29; 3:13-17; Rom. 5:8; 8:32; 2 Cor. 5:19-21; 8:9; Phil. 2:5-8).
The moment of truth regarding the doctrine of the Trinity came at the Council of Nicaea (A.D.325), when the church countered the Arian idea that Jesus was God’s first and noblest creature by affirming that he was of the same “substance” or “essence” (i.e., the same existing entity) as the Father. Thus there is one God, not two; the distinction between Father and Son is within the divine unity, and the Son is God in the same sense as the Father is. In saying that Son and Father are “of one substance,” and that the Son is “begotten” (echoing “only-begotten,” John 1:14, 18; 3:16, 18, and NIV text notes) but “not made,” the Nicene Creed unequivocally recognized the deity of the man from Galilee.
A crucial event for the church’s confession of the doctrine of the Incarnation came at the Council of Chalcedon (A.D.451), when the church countered both the Nestorian idea that Jesus was two personalities—the Son of God and a man—under one skin, and the Eutychian idea that Jesus’ divinity had swallowed up his humanity. Rejecting both, the council affirmed that Jesus is one divine-human person in two natures (i.e., with two sets of capacities for experience, expression, reaction, and action); and that the two natures are united in his personal being without mixture, confusion, separation, or division; and that each nature retained its own attributes. In other words, all the qualities and powers that are in us, as well as all the qualities and powers that are in God, were, are, and ever will be really and distinguishably present in the one person of the man from Galilee. Thus the Chalcedonian formula affirms the full humanity of the Lord from heaven in categorical terms.
The Incarnation, this mysterious miracle at the heart of historic Christianity, is central in the New Testament witness. That Jews should ever have come to such a belief is amazing. Eight of the nine New Testament writers, like Jesus’ original disciples, were Jews, drilled in the Jewish axiom that there is only one God and that no human is divine. They all teach, however, that Jesus is God’s Messiah, the Spirit-anointed son of David promised in the Old Testament (e.g., Isa. 11:1-5; Christos, “Christ,” is Greek for Messiah). They all present him in a threefold role as teacher, sin-bearer, and ruler—prophet, priest, and king. And in other words, they all insist that Jesus the Messiah should be personally worshiped and trusted—which is to say that he is God no less than he is man. Observe how the four most masterful New Testament theologians (John, Paul, the writer of Hebrews, and Peter) speak to this.
John’s Gospel frames its eyewitness narratives (John 1:14; 19:35; 21:24) with the declarations of its prologue (1:1-18): that Jesus is the eternal divine Logos (Word), agent of Creation and source of all life and light (vv. 1-5, 9), who through becoming “flesh” was revealed as Son of God and source of grace and truth, indeed as “God the only begotten” (vv. 14, 18; NIV text notes). The Gospel is punctuated with “I am” statements that have special significance because I am (Greek: ego eimi) was used to render God’s name in the Greek translation of Exodus 3:14; whenever John reports Jesus as saying ego eimi, a claim to deity is implicit. Examples of this are John 8:28, 58, and the seven declarations of his grace as (a) the Bread of Life, giving spiritual food (6:35, 48, 51); (b) the Light of the World, banishing darkness (8:12; 9:5); (c) the gate for the sheep, giving access to God (10:7, 9); (d) the Good Shepherd, protecting from peril (10:11, 14); (e) the Resurrection and Life, overcoming our death (11:25); (f) the Way, Truth, and Life, guiding to fellowship with the Father (14:6); (g) the true Vine, nurturing for fruitfulness (15:1, 5). Climactically, Thomas worships Jesus as “my Lord and my God” (20:28). Jesus then pronounces a blessing on all who share Thomas’s faith and John urges his readers to join their number (20:29-31).
Paul quotes from what seems to be a hymn that declares Jesus’ personal deity (Phil. 2:6); states that “in Christ all the fullness of the Deity lives in bodily form” (Col. 2:9; cf. 1:19); hails Jesus the Son as the Father’s image and as his agent in creating and upholding everything (Col. 1:15-17); declares him to be “Lord” (a title of kingship, with divine overtones), to whom one must pray for salvation according to the injunction to call on Yahweh in Joel 2:32 (Rom. 10:9-13); calls him “God over all” (Rom. 9:5) and “God and Savior” (Titus 2:13); and prays to him personally (2 Cor. 12:8-9), looking to him as a source of divine grace (2 Cor. 13:14). The testimony is explicit: faith in Jesus’ deity is basic to Paul’s theology and religion.
The writer to the Hebrews, purporting to expound the perfection of Christ’s high priesthood, starts by declaring the full deity and consequent unique dignity of the Son of God (Heb. 1:3, 6, 8-12), whose full humanity he then celebrates in chapter 2. The perfection, and indeed the very possibility, of the high priesthood that he describes Christ as fulfilling depends on the conjunction of an endless, unfailing divine life with a full human experience of temptation, pressure, and pain (Heb. 2:14-17; 4:14-5:2; 7:13-28; 12:2-3).
Not less significant is Peter’s use of Isaiah 8:12-13 (1 Pet. 3:14). He cites the Greek (Septuagint) version, urging the churches not to fear what others fear but to set apart the Lord as holy. But where the Septuagint text of Isaiah says, “Set apart the Lord himself,” Peter writes, “Set apart Christ as Lord” (1 Pet. 3:15). Peter would give the adoring fear due to the Almighty to Jesus of Nazareth, his Master and Lord.
The New Testament forbids worship of angels (Col. 2:18; Rev. 22:8-9) but commands worship of Jesus and focuses consistently on the divine-human Savior and Lord as the proper object of faith, hope, and love here and now. Religion that lacks these emphases is not Christianity. Let there be no mistake about that!
From J.I. Packer’s: Concise Theology: A Guide To Historic Christian Beliefs