John provides a description of Jesus and then records the demands of the Saviour.
The first detail that John mentions about Jesus is that he is like a son of man. We might assume that John is pointing to the humanity of Jesus here, and that is true. Yet he has a special kind of humanity, one that is marked by unique abilities. Our minds should be drawn to the prophecy of Daniel 7 in which one like the Son of man received a kingdom from God the Father, which happened to Jesus when he ascended. So what we have here is a description of the ascended Saviour.
Another suggestion that is made regarding the white hair is that it points to purity or holiness of character, and it is the case that often in the Book of Revelation the colour white means holiness (as in the white robes that are mentioned). Our thoughts can go to what the seraphim say about Jesus in Isaiah 6, ‘Holy, holy, holy.’ The one who searches the churches is wise and holy.