Assuming, with the Hebrew scriptures, that God reveals himself to those he has created, the Gospel of John proclaims Jesus to be the culmination of the self-revelation of God, not only in his glorious signs but also precisely in his death and his return to heaven.
The Gospel of John, particularly the prologue, exercised a disproportionate influence in the patristic period on the development of the central dogmas of Christianity, those of the Trinity and of the Two Natures of Christ. The opening statements (1:1-2) envisage the presence of God’s word from the beginning of eternity; they are followed by further assertions that the Word was God’s agent in creating the world (1:3-5). The complex concept of a fellowship of discrete, permanent entities sharing in the unity of the indivisible divine being, which sprung from and built on the matrix of Jewish monotheism, led, after further reflection on the relation of the Holy Spirit to the Father and the Son, to the trinitarian formula of Nicaea 325 (“one essence [ousia], three persons [hypostaseis]”).
Likewise John’s simple statement “The Word became flesh” (1:14) begged for elaboration and remains the chief proof-text for the orthodox Christian doctrine that the Logos, without surrendering his essential deity, assumed an intact human nature, body and mind, in becoming incarnate in Jesus of Nazareth: not two persons, but two natures perfectly united in one person, without diminution or change, admixture, or confusion of the attributes of either nature. Only on such a view of the person of Christ can it be maintained that it was by the sacrifice of a genuine, representative human life that the human race was delivered from divine wrath due to sin and that it was an act of God that brought about the redemption.
“Eternal life” is the benefit that the cross secured for those who believe. The phrase refers to a life that, once begun, will last forever; but it also emphasizes a qualitative fullness of life, a life that is free and abundant, a sort of life that is not yet wholly in evidence on earth but will obtain in the age to come. Eternal life, however, is not merely awaited: The Gospel suggests that by believing in Jesus, people can taste it now, and it becomes a present experience.