Because free gifts can and do come with conditions. Yet working to meet those conditions do not earn anything.
In Jn 6:27 it says Jesus GIVES everlasting life, it's free for He gives it. Since He gives it for free why did He say to labour for it? Because Jesus is the gift giver and has the right to place conditions upon His free gift. There is nothing written anywhere that says Jesus must give His free gift UNCONDITIONALLY, Jesus has the right to put CONDITIONS upon His free gift.
Again, Naaman worked for his healing by going and dipping so does that means he earned his healing therefore grace had NOTHING to do with it?
Abraham was saved the same way as Naaman, as for that matter, you and I are saved the same way as Abraham and Naaman.
Was Abraham saved by obeying God and leaving his homeland to a country God would show him? Was Abraham saved by anything he outwardly did in obeying God (works)? No, certainly not! I know this because the Bible says, "Abraham believed God and it was accounted unto him for righteousness." In like manner was Naaman also saved. It was his belief that saved him, not anything he did.
I believe the question was, would Naaman have been saved if he hadn't dipped in the Jordan? No he would not. It would have proved his unbelief. But when Naaman made the decision (faith) to do as the prophet of God instructed, he was saved. Naaman was saved before he even stepped into the water, as Abraham was saved before he ever left the Ur of Chaldees to the land promised by God. It is by faith that we are saved, not of works.
We work because we are saved, not to get saved. Paul makes this clear in Rom. 11:6, he makes a sharp contrast between faith and works:
"And if by grace, then
is it no more of works: otherwise grace is no more grace. But if
it be of works, then is it no more grace: otherwise work is no more work."
Grace cannot be mixed with works or works mixed with grace. They are contrary to one another.
It is impossible for Naaman to have been saved by faith and dipping in the Jordan. It was his faith alone that saved him.