Sometime near the end of the first century, a write skilled in Greek language and philosophy wrote the last Gospel, called the Gospel According to John. In some quarters the authorship is assigned to the Apostle John, while others declare it was another person, perhaps another person named John. While the authorship is a hotly debated item, what is not debated is this Gospel is very different than the first three. 

This Gospel is far more philosophical; and contains longer and deeper theological expressions by Jesus. In the Synoptic Gospels;  Matthew, Mark and Luke, Jesus speaks in quick bursts and uses parables for many of his teachings. Here we have philosophical explanations by Jesus; about the Kingdom of heaven and who he is.