וַיֹּ֤אמֶר דָּוִד֙ אֶל־הַגִּבְעֹנִ֔ים מָ֥ה אֶעֱשֶׂ֖ה לָכֶ֑ם וּבַמָּ֣ה אֲכַפֵּ֔ר וּבָרְכ֖וּ אֶת־נַחֲלַ֥ת יְהוָֽה׃
and David said unto the Gibeonites: ‘What shall I do for you? and wherewith shall I make atonement, that ye may bless the inheritance of the LORD?’
Read Kabbalistic (mystical) interpretations of II Samuel 21:3: Zohar and classical Jewish mystical sources, free online.