24 My truth and my mercy shall be with him. God shows that he will continue to exercise without intermission that grace which he had manifested towards David at first. These words are as if he had said, that to prove himself faithful to his word, he would be always gracious and bountiful. Thus We see that God, not only at the outset, furnished David with testimonies of his goodness, but that he always continued to deal with him in the same merciful way. This has a reference to the whole Church of Christ, so that the divine goodness is manifested in the whole course of our salvation, and not only at our first entrance upon it, as these shufflers and sophists the Sorbonists foolishly talk. (543) The horn of David denotes here, as it often does in other places, his glory, dignity, and power. The meaning therefore is, that by the grace of God, this kingdom shall always flourish and prosper.
(543) “ I will make him my first-born; i. e. , as the eldest son of a family ranks the highest, and receives the most from his father, so shall David be first in the order of kings, who, when they are legitimate sovereigns, may be regarded as the sons of God, their common Father: comp. Genesis 27:1, etc.; Exodus 4:22; Deuteronomy 21:17; Psalms 2:7; Colossians 1:15. In Isaiah 14:30, by the first-born of the poor, is meant the extreme of that class, they who are the poorest of the poor.” — Cresswell.