For all the promises of God in him - All the promises which God has made through him. This is another reason why Paul felt himself bound to maintain a character of the strictest veracity. The reason was, that God always evinced that; and that since none of His promises failed, he felt himself sacredly bound to imitate Him, and to adhere to all His. The promises of God which are made through Christ, relate to the pardon of sin to the penitent; the sanctification of his people: support in temptation and trial; guidance in perplexity; peace in death, and eternal glory beyond the grave. All of these are made through a Redeemer, and none of these shall fail.
Are yea - Shall all be certainly fulfilled. There shall be no vacillation on the part of God; no fickleness; no abandoning of his gracious intention.
And in him amen - In Revelation 3:14, the Lord Jesus is called the “Amen.” The word means true, faithful, certain. And the expression here means that all the promises which are made to people through a Redeemer shall be certainly fulfilled. They are promises which are confirmed and established, and which shall by no means fail.
Unto the glory of God by us - Either by us ministers and apostles; or by us who are Christians. The latter, I think, is the meaning; and Paul means to say, that the fulfillment of all the promises which God has made to His people shall result in His glory and praise as a God of condescension and veracity. The fact that He has made such promises is an act that tends to His own glory - since it was of His mere grace that they were made; and the fulfillment of these promises in and through the church, shall also tend to produce elevated views of His fidelity and goodness.