Naaman declares that all the gods of Aram are no gods at all. But he still thinks in terms of “Do ut des” (Latin; this is a religious worldview that entails, “I give you a present and you (my god) will give me your blessing”). This is the reason why he is sending so many precious gifts. Therefore, he wants Elisha to accept a gift on behalf of the God of Israel.
15 Then he returned to the man of God, he and all his company, and he came and stood before him. And he said, “Behold, I know that there is no God in all the earth but in Israel; so accept now a present from your servant.”