Thy mercy, O LORD, is in the heavens; and thy faithfulness reacheth unto the clouds. Thy mercy, O Lord, is in the heavens - That is, thou art abundant, infinite in thy mercy; else such transgressors must be immediately cut off; but thy long-suffering is intended to lead them to repentance.
Thy faithfulness reacheth unto the clouds - עד שחקים ad shechakim, to the eternal regions; above all visible space. God's faithfulness binds him to fulfill the promises and covenants made by his mercy. Blessings from the heavens, from the clouds, from the earth, are promised by God to his followers; and his faithfullness is in all those places, to distribute to his followers the mercies he has promised.