And when Nathan the Prophet came and rebuked David for that act, he said (Ibid. 13) "I have sinned to the L-rd," and (Psalms 51:3) "Be gracious (chaneini) to me, O G-d, according to Your lovingkindness … (6) To You alone have I sinned and what is evil in Your eyes have I done."
Two goodly leaders rose up for Israel — Moses and David king of Israel — and they could have asked for reward on the basis of their good deeds, but they asked of the Holy One Blessed be He only that he "grace" them, (this being the thrust of "chaneini" and of "va'etchanan"). Now does this not follow a fortiori, viz.: If these, who could have asked for reward on the basis of their good deeds, asked of the Holy One Blessed be He only that He "grace" them, then we, who are not even a thousandth of the thousands and ten thousands of his disciples, how much more so should we ask of the L-rd only that He "grace" us!