What themes appear in John's prologue that appear throughout his Gospel that make it unique from the other Gospels in the New Testament?
The prologue of John presents the thesis of the book which is that Jesus is "the Logos or the Word."The term, Word," conveys the notion of divine self-expression or speech and has a rich Old Testament background.When Jesus speaks, God is speaking. When God speaks things come into being (Genesis 1:3) and by speech God relates personally to his people (e.g. Genesis 15:1). Jesus is the living active Word that created the universe and gave order to it. The prologue emphasizes themes that will occur throughout the gospel: Christ's deity (1:1), the incarnation (1:14), the response to his coming by reacting in belief or unbelief (1:11, 12), the work of Christ to reveal God the Father to mankind (1:18) and Christ's mission to redeem mankind (1:12).
One important term found in the prologue is the word "believe." It is used 98 times in the gospel with the essential meaning of trusting in Christ or committing one's life to Christ. Indeed the very purpose of the book is found in John 20:30-31. "belief in Jesus, the Messiah and Son of God." Chapters 1 through 12 focus in on signs or miracles that attest to Christ deity and give reason for believing that he is fully God and fully man in one person.
The fact that in him is life (1:4), that he originates and gives life, will later be declared in John 14:6 when he states that he is "the way, the truth, and the life." One must go through him to get to the Father.
The fact that he is light (1:4, 5) declares that he brings to this dark world true knowledge, perfect moral purity, and the light that shows the very presence and essence of God. He will later declare that he is the "Light of the World" in John 8:12.
We see then in the prologue the great themes of the gospel - the incarnation, the deity of Christ, belief and unbelief, light and darkness.
The thing about the Gospel written by the Apostle John is that his themes enumerate the attributes of the Christ, Jesus. He begins with Christ's being the Word and Light and Life and, as he unfolds his proof's of Jesus divinity, he includes several others like Bread of Life and Living Water.