He wasn't used to being treated this way. He was used to being treated with respect. So, his pride caused him to become angry and he refused to dip in the river. Fortunately for him, one of his servants had the nerve and cared enough about him to talk to him about his decision. He changed his mind and went and dipped in the Jordan and when he came up his flesh was clean as a little child's. He was healed. Proverbs 16:18, "Pride goeth before destruction." If he had continued to let his pride take over, he would have died a leper.
There may come a time in your life when God may call you to do something that your pride doesn't want you to do. If that is the case, remember Naaman. He might have died because of pride. Don't let your pride hinder anything the Lord wants you to do. Even if it seems ridiculous, if you know it's from God, do it.