Charles H. Spurgeon on Psalms 89:28

My mercy will I keep for him for evermore. The kings of David's line needed mercy, and mercy prevented their house from utterly perishing until the Son of Mary came. He needs no mercy for himself, but he is a representative man, and the mercy of God is required for those who are in him: for such mercy is kept for ever. And my covenant shall stand fast with him. With Jesus the covenant is ratified both by blood of sacrifice and by oath of God, it cannot be cancelled or altered, but is an eternal verity, resting upon the veracity of one who cannot lie. What exultation fills our hearts as we see that the covenant of grace is sure to all the seed, because it stands fast with him with whom we are indissolubly united.