John Gill Bible Commentary

If thy children will keep my covenant, and my testimony that I shall teach them,.... The former part of the promise and oath is absolute, respecting the Messiah; but this is conditional, and relates to the seed of David, both immediate, and in succeeding generations; proposing their observance of the law of God, as the condition of their enjoying the kingdom after him. By the "covenant" and "testimony" are meant the same thing; the law, which was given to the people of Israel in the form of a covenant, and was a testimony of the will of God to them: in this the kings of Israel were to read continually, and conduct according to it in their personal walk and conversation, and by it to rule the people they were set over; and which the Lord promises to teach them by his prophets, whose business it was not to promulgate new laws, but to explain what were given. Now in case this was attended to, and the instructions of prophets observed, then thus it would be, their children also shall sit upon thy throne for evermore; but, the condition not being fulfilled, this did not take place: Solomon, his immediate successor, fell into idolatry in the latter part of his life; and Rehoboam, his son, slighted the advice of the old men, founded upon the laws of God, and ten tribes revolted from him: several succeeding kings of Judah, of the house of David, were very wicked princes; and the race of them ended in Zedekiah, who was carried captive into Babylon. Indeed all this is true of Christ and his spiritual offspring; he kept the covenant of grace made with his divine Father; and the law or testimony; and fulfilled it in the room and stead of his people; and did the whole will and work of his Father, and in all things pleased him: and his children also lay hold by faith on the covenant and the promises of it; and receive, observe, and retain the testimony of the Gospel; and shall reign with Christ, on the same throne with him, for ever and ever.