One who believes in the Son has eternal life, but one who disobeys{The same word can be translated "disobeys" or "disbelieves" in this context.} the Son won't see life, but the wrath of God remains on him."

 So then belief in Jesus has these three elements--belief that God is our loving Father, belief that Jesus is the son of God and therefore tells us the truth about God and life, and unswerving and unquestioning obedience to Jesus. 