To the Lord our God belong mercies and forgivenesses, though we have rebelled against him;
To the Lord our God belong mercies - the plural intensifies the force: mercy manifold, and exhibited in countless ways. As it is humbling to recollect "righteousness belongeth unto God" (Daniel 9:7), so it is comforting that "mercies also belong to the Lord OUR God."
Though we have rebelled against him - rather, since, etc. (Vulgate.) Our only hope must now be, not our righteousness, of which we have none, but His "mercies;" "for we have rebelled against Him" Since we have stoned so greatly, there will be a large field for the exercise of His mercies. So David pleads, "For thy name's sake, O Lord, pardon mine iniquity, FOR it is great." Or else it is an answer to the tacit objection, If mercies belong to Him, how, then, is it that He had given up His people to such miseries? The answer is, He has been driven to it by our rebellion (Grotius). Our punishment is not inconsistent with His "mercies," since we have rebelled against Him.