"He who comes from heaven is more important than anyone else"
John means that Jesus is greater than he is since Jesus is from heaven, and John was born on the earth. AT: "He who is born in this world is like everyone else who lives in the world and he speaks about what happens in this world" (See: rc://en/ta/man/translate/figs-metonymy)
This means the same thing as the first sentence. John repeats this for emphasis.
John is speaking about Jesus. AT: "The one from heaven tells about what he has seen and heard in heaven"
Here John exaggerates to emphasize that only a few people believe Jesus. AT: "very few people believe him" (See: rc://en/ta/man/translate/figs-hyperbole)
"Anyone who believes what Jesus says"
"proves" or "agrees"