A number of key terms used throughout John's Gospel can almost all be found in the prologue, and thereby bolster the thesis that the prologue summarizes the whole. As we have seen, the "Word" or logos is the creative element and revelation of God himself incarnate in Christ. Logos is for the Greeks the rational principle of reality, for the Hebrews the principal agent of creation (as revealed in Genesis 1), and for the early church the message of salvation - meanings all encapsulated in verse 1 of John and paralleled in Hebrews 1:1-2. The term "know" (whether ginosko or oida in Greek) is used a total of 118 times in John, and can refer to both subjective and objective knowledge. John indicates in verse ten and eleven of chapter one, as throughout the Gospel, that real knowledge belongs to those who believe and receive Christ rather than to worldly philosophers or even the scribes. "Life" (zoe, or spiritual, eternal life) is another important term in John's theology, as it is taken most literally: Christ is life itself, so that those who don't believe in him are dead in a very real sense. "In Him was life, and the life was the light of men" (v. 4). Similarly, Jesus as logos is the "truth" incarnate (v. 14, cf John 14:6). On the heels of his post-resurrection accounts, John also indicates that "belief" is central to the purpose of the Gospel: "...but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name" (John 20:31). That same thought is expressed in verse twelve of the prologue: Jesus gave the right to become children of God "to those who believe in His name." Finally, there are frequent appeals in John to the "witness" of third parties to substantiate the claims of the Gospel, in compliance with the OT requirement: "By the mouth of two or three witnesses the matter shall be established" (Deut. 19:15). The OT Scripture itself (or "Moses"), the disciples, the multitude, the Spirit, and the Father all bear witness to the authority of Christ. In the prologue John invokes the witness of John the Baptist: "This man came for a witness, to bear witness of the Light, that all through Him might believe" (v. 7).
One of the keys of interpretation has to do with ascertaining the particular circumstances in which the author wrote, or the historical-cultural context. Certain polemical elements in John's writings, along with much related historical evidence, indicate that his presentation of Christ has been inspired at least to an extent by conflict. Much of his Gospel, like the Synoptics in this regard, is taken up with polemics against the Jews, or more precisely the powerful leaders of the Jews: the Pharisees, the Sadducees and the Sanhedrin. In their general hostility to the message of Christ, the Jewish leaders represent the secular world as well. (Notice how careful John is to record the direct involvement of both Jews and Romans in the crucifixion of Christ, for instance.) Though the conflict develops more vividly in later chapters, John alludes to it in verse eleven of chapter one: "He came to His own, and His own did not receive Him" - and again in verse seventeen: "For the law was given through Moses, but grace and truth came through Jesus Christ." Among the Gentiles, Gnosticism was one of the earliest and most formidable heresies to face the early church, taking on two main forms: Docetism and Adoptionism. John goes to some lengths to repudiate both strains of Gnosticism in the Gospel and in his letters, especially 1 John. In the prologue of John, he describes in no uncertain terms the spiritual, eternal divinity of Christ (v. 1-3), as against the Adoptionists, and then proceeds to declare that the same divinity has been fully embodied in human flesh (v. 14), in repudiation of the Docetists. Textual and historical evidence also points to the existence in the apostle's day of a John the Baptist sect (John 1:21-23; 3:27-30), which maintained itself long after John the Baptist's ministry and death (Acts 19:1-3). Like certain Christians today who preach condemnation, these devout followers of John the Baptist seem to have either doubted or ignored the central message of their master. John the apostle subtly counters their influence by way of reminder: "There was a man sent by God, whose name was John. This man came for a witness, to bear witness of the Light.... He was not that Light, but was sent to bear witness of that Light" (John 1:7-8).
Scholars are divided over the issue of authorship, but most generally agree that John's Gospel was written in stages: (1) The document was originally drafted in light of the testimony of an original apostolic witness - whether actually written by John the apostle himself or by another John, "the Elder" (as he designates himsef in 1 and 2 John). Textual evidence in light of Palestinian archaeology favors the "traditional" theory of Irenaeus, citing Polycarp, that the Fourth Gospel was written by John the apostle of Christ, the son of Zebedee, at Ephesus. (Or at least that theory seems to fit better with the facts than the alternative view attributed to Papias by Eusebius, that the anonymous "Elder" wrote from Asia Minor after the Apostle John was already dead.) (2) The core material of the Gospel was subjected to a process of theological development, or redaction, with clear polemical objectives in mind (John 20:31) - which indicates a retroactive or reflective viewpoint. (3) Some would also argue that John was further polished by an editorial group from Ephesus, as indicated by a reference to the first person plural in John 21:24: "and we know that his testimony is true." As a whole, the high theological development of the prologue itself is evidence at least of the Johannine feature of reflection. This would further lend support to the view that John underwent a number of developmental phases.