The Gospel according to John was written near the end of the first century A.D. It’s a beautiful supplement to the first three books of the New Testament.
For example, The book of John provides us with considerable information about Christ’s ministry in Judea. The first three, or synoptic, Gospels say very little about Jesus’ work in Judea. John includes none of the synoptic parables, but recounts several controversial discourses Jesus presented in the Temple at Jerusalem. This Gospel also includes several of Jesus’ miracles that are recorded nowhere else in Scripture.
Another interesting feature of John’s Gospel is the attention that’s given to the symbols Christ used in His teaching—water, bread, light, sheep, the grapevine, and others.
But the apostle John’s primary purpose in writing this Gospel was that his readers might believe that Jesus is the Christ, the Son of God, and that believing they might have life through His name. (See John 20:31.)