The Gospel of John, (literally, According to John; Greek, Κατά Ιωαννην, Kata Iōannēn) is the fourth gospel in the canon of the New Testament, traditionally ascribed to John the Evangelist. Like the three synoptic gospels, it contains an account of some of the actions and sayings of Jesus, but differs from them in ethos and theological emphases. The purpose is expressed in the conclusion, 20:30-31: "...these [Miracles of Jesus] are written that you may (come to) believe that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name. The book hinges on the seven signs Jesus performed and ends with the Passion of the Lord.
(Summary from Wikipedia adapted by Sam Stinson).