The connecting word "but" contrasts Naaman's prestigious position of army commander, with his having this terrible disease. (See: [[rc://en/ta/man/translate/writing-connectingwords]])
This means that people had told Naaman that Elisha was able to perform miracles. Here Elisha is used to represent the miracles that God gave Elisha the power to perform. (See: [[rc://en/ta/man/translate/figs-metonymy]])