Only one of Jesus’ closest followers dared call himself “the beloved disciple.” John used this description of himself not because he thought he was the favourite, or better than the others; but because he could hardly believe the gracious love and humility of God that allowed him to see and know the Son of God, Jesus Christ, in the flesh. You cannot read John’s gospel without something of the same sense of amazement. The last four chapters of the gospel are full of searching questions (over 30) as Jesus finishes the work God the Father sent him to accomplish. Questions of identity and power, of truth and love, of love and hate, and above all, of faith and unbelief. John does not want us to stop at amazement; nor to just experience “faith.” He wants us to believe something and so have life, eternal life.
This is very different from the vague and misleading encouragements to merely “believe” or to just “have faith.” Far more important than the quality of our faith is the object of our faith: he wants us to “believe that.” This is why John writes.