If someone claims to be able to heal diseases that he himself has, there is no reason to believe he is really a doctor. People will speak this proverb to Jesus to say that they will only believe he is a prophet if they see him do what they have heard that he did in other places. (See: [[rc://en/ta/man/jit/writing-proverbs]])
The people of Nazareth do not believe Jesus is a prophet because of his low status as Joseph's son. They will not believe unless they personally see him do miracles.