Have mercy upon me, O God, according to thy loving-kindness. It is observable that the whole psalm is addressed to God (Elohim), and not to Jehovah (the "Lord" in Psalms 51:15 is Adonai), as though the psalmist felt himself unworthy to utter the covenant-name, and simply prostrated himself as a guilty man before his offended Maker.
It is not correet to say that "loving-kindness implies a covenant" (Cheyne), since God is "good to all, and his tender mercies are over all his works" (Psalms 145:9). According unto the multitude of thy tender mercies blot out my transgressions.
David's first prayer is for pity; his second, to have his offences "blotted out," or "wiped out"—entirely removed from God's book (comp. Exodus 32:32; Isaiah 43:25; Isaiah 44:22). He says "my transgressions," in the plural, because "his great sin did not stand alone—adultery was followed by treachery and murder" (Canon Cook).