In this verse the KJV is much more accurate than the NASB. “Mercy” (loyalty, righteousness NASB) (2617a) is used twice in the KJV. This is because it is the same word in Hebrew. For some stylistic reason the NASB uses two different words.
This word in Hebrew is chesed. To me it is the OT equivalent of the Greek agape. I think the best translation is “lovingkindness.” It is at the heart of how God deals with us but notice that it is not clear who is extending this quality. Is this a case of God extending mercy to preserve or the king being preserved because he is merciful?
I think this is another case of both/and not either/or. It starts with God. He is the source. He is the example. He is the demander.
(1 John 4:19 KJV) We love him, because he first loved us.He supplies, we apply. He gives, we pass on.
So? Be a channel that God can use. Pass it on.