Abigail is stating that if David chooses not to take revenge he will have a clear conscience when Yahweh makes him king of Israel. This can be stated in positive form. Alternate translation: "You will always be glad you acted as you did" (See: [[rc://en/ta/man/translate/figs-litotes]])
# my master ... himself ... my master ... your servant
Abigail speaks of herself and David as if they are two other people, to show that she respects David. "you ... yourself ... you ... me" (See: [[rc://en/ta/man/translate/figs-pronouns]])