Before I spend any time looking into the Hebrew, I find that I like the NASB better than the KJV on this verse. As usual, when I look a little deeper it is a mixed bag. Although you might stretch the Hebrew to mean “tranquil” (4832) the KJV’s “sound” is much better. The word means healthy and being made well. A good example is,
(Mal 4:2 KJV) But unto you that fear my name shall the Sun of righteousness arise with healing (4832) in his wings; and ye shall go forth, and grow up as calves of the stall.This would have obvious applications about the spiritual healing that comes through regeneration and is thus applied to our physical well-being.
The second part I give to the NASB. “Passion” (7068) is better than “envy”. The picture given by the NASB does a better job of putting the picture together. God wants us to be calm and secure in our minds because we trust Him. We are not to go off in wild flights of temper.
So? For some the change is instant. For some it is a life long discipline. Some people are just born easy going. It is part of living a righteous life.