Naaman is cured and shows gratitude and humility. There is still however some of the old traditional theology left in him.
We first see that he wants to give a gift to Elisha, probably simply from gratitude but Elisha is careful not to take the gift as that would appear to be selling God's favor. This was a very common practice with the pagan worship, an offering was always made to the priest for services. I have a theory on that too, I believe that demons will inflict people and then stop inflicting people so as to cause confusion and keep them from the true God. So a person who is suffering from something could possibly appear to be healed when going to a pagan priest. But this is a different case, Naaman was fully healed and all that he did was be obedient. We see more of the old theology as Naaman asks for two mules loaded with dirt. It was believed that gods were regional, that the God of Israel was associated with the soil of Israel so Naaman needed some of that dirt to build an altar. Verses 18 and 19 show a conflict of conscience. Naaman now knows the gods of Syria are false gods yet part of his duties include accompanying his master to those temples. He knows that it's wrong yet refusal could cost him his station or life. The prophet simply tells him to go in peace. Both had limited knowledge and understanding, Naaman certainly did not know The Law, he simply experienced grace. I would be interested to know if his experience converted anyone else in Syria through the rest of his life, or if he found a way to avoid the pagan temples.