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]])
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]])