11. So shall my word be. The word goeth out of the mouth of God in such a manner that it likewise “goeth out of the mouth” of men; for God does not speak openly from heaven, but employs men as his instruments, that by their agency he may make known his will. But the authority of the promises is more fully confirmed, when we are told that they proceed from the sacred mouth of God. Although, therefore, he brings forward witnesses from the earth, he declares that all that they have promised shall be ratified and sure; and, in order to impress more deeply on the minds of men the power and efficacy of preaching, he declares that he does not cast that precious seed at random, but appoints it for a fixed purpose, and consequently that we ought to entertain no doubt as to the effect; for there is nothing to which mortals are more prone than to judge of God from themselves so as to withhold belief from his voice.
This doctrine must be frequently repeated and inculcated, that we may know that God will do what. he hath once spoken. For this reason, when we hear the promises of God, we ought to consider what is his design in them; so that, when he promises the free pardon of our sins, we may be fully assured that we are reconciled through Christ. But, as the word of God is efficacious for the salvation of believers, so it is abundantly efficacious for condemning the wicked; as Christ also teacheth, “The word which I have spoken, that shall judge him at the last day.”