Through the years, the Fourth Gospel has led countless ordinary Christians to extraordinary heights of personal devotion and has inspired masterpieces of theology, music, art, and literature. Not least influential have been its powerful themes, among which are light, love, truth, and glory. All four of these converge on Jesus, who is the expression of God's love (3:16), who is the Light of the World (8:12), who is the Truth (14:6), and who both brings glory to God (14:13) and receives glory from God (12:28).
This gospel also has a good deal to say about the Spirit. It teaches that Jesus himself bore the Spirit (1:32-33; 3:34), that he both promised the Spirit (as the Counselor) and portrayed his functions (14:15-17, 26; 15:26; 16:5-15), and that he bestowed the Spirit (20:22). The Spirit's presence also marks the church. Without the Spirit there is no new birth and no entry into the kingdom of God (3:3-5). It is the Spirit who mediates life (6:63; cf. 7:38) and is effective in Christian worship (4:23-24). The Spirit is the power behind the church and the source of its authority; by receiving the Spirit, the church is equipped for its mission (20:21-23). The detailed teaching is in the passages on the Counselor (14:15-17, 26; 15:26; 16:5-15). The Fourth Gospel makes it plain that the Spirit is no option for the church.
Four major themes of John's gospel come together in 20:30-31, where the author states his purpose in writing. The first is a reference to the miraculous signs recorded in the gospel. In John the word signs regularly designates Jesus' miraculous works, which, as evidences (signs) of who he is, become pointers to faith in him (e.g., 2:11; 4:53-54; 6:14; 7:31). A second theme is that of belief in Jesus. Belief is the source of salvation, unbelief of condemnation (3:14-18). Life, the sure issue of belief, is yet a third theme. John 3:16 exalts this idea; so do many other texts in John.
This brings us to the fourth theme mentioned in 20:30-31, the identity of Jesus himself. As Christology is central to John, central to Johannine Christology are two dominant paradoxes: the paradox of Jesus' unity with and distinction from God and the paradox of his simultaneous deity and humanity. These particular verses underscore his relationship to God, whose Son he is.
The unity of Jesus with God is addressed at the very beginning of the Gospel. Jesus is the incarnation of the Word (1:14 and context; cf. 1:18) who both was God (vv. 1-2) and was responsible for creation (vv. 3, 10). But Word theology, as an expression of the link between Jesus and God, occurs only in the opening section. The fundamental Johannine designation of their relationship and of their unity is Father and Son. As Son, Jesus is very close to the Father. He does what the Father does and only what the Father does (5:17; 19). He judges rightly because in his judging he is in agreement with the Father (8:16; cf. 5:30). And his working in accordance with God's will is absolute: the purpose of his mission is to do the will of the one who sent him (6:38); the denouement of his life would make it plain that he acted precisely as taught by the Father (8:28); even the laying down and taking up again of his life are dependent on the Father's command (10:18). So close are Jesus and his Father that he can reassure Philip and the perplexed disciples that to see him is to have seen the Father (14:9; cf. 12:45); he can inform the Pharisees that, if they would, they could know the Father through him, because to know him is to know the Father (8:19); and he can berate the Jews for their unbelief in the Father, because it is belief in Jesus that equals belief in God (12:44). And eternal life, which consists in knowing the only true God, has as a second element knowing Jesus Christ (17:3).
It is part of the method of John's gospel that we are allowed to watch individuals and groups struggling with the question of Jesus' identity. The matter of Jesus' physical origin and its implications for various individuals is a good case in point. In the beginning, when Philip identifies Jesus of Nazareth as the one of whom Moses and the prophets spoke, Nathaniel responds with incredulity; yet he acts on Philip's simple invitation to come and see for himself and is convinced (1:45-51). He, like the man born blind (9:1-38), comes to see and so comes to believe. Others, however, use knowledge of Jesus' Galilean home as a way of not acknowledging his claims (7:40-43, 50-52). As the text makes clear, some are self-blinded (e.g., 9:39-41).
These passages raise the question of Jesus' messiahship. Deity is at issue in 5:18 and 10:33. In both places he is charged with claiming to be, or making himself equal to, God. Neither charge is rebutted; for, though Jesus was not exactly making himself equal to God, the author does not want to say that he is not God. In fact, his own understanding is reflected in two passages that bracket the gospel. The first is the opening assertion of deity for the Word and thus for Jesus (1:1-2). The second is Thomas's spontaneous worship of the resurrected Jesus with language no faithful Jew would ever ascribe to any but God Almighty (20:28).