Albert Barnes Commentary 2 Kings 5:14

"Then went he down, and dipped [himself] seven times in the Jordan, according to the saying of the man of God; and his flesh came again like unto the flesh of a little child, and he was clean." — 2 Kings 5:14 (ASV)

Seven times - Compare 1 Kings 18:43. In both cases, a somewhat severe trial was made of the individual’s faith. Compare the seven marches around Jericho, and the sudden fall of its walls (Joshua 6:3–20).