30. Their seed shall serve him. The more to exalt the greatness of the benefit, he declares that it will be of such a character that posterity will never forget it. And he shows how it will come to be perpetuated, namely, because the conversion of the world, of which he has spoken, will not be for a short time only but will continue from age to age. Whence we again conclude, that what is here celebrated is not such a manifestation of the glory of God to the Gentile nations as proceeds from a transitory and fading rumor, but such as will enlighten the world with its beams, even to the end of time. Accordingly, the perpetuity of the Church is here abundantly proved, and in very clear terms: not that it always flourishes or continues in the same uniform course through successive ages, but because God, unwilling that his name should be extinguished in the world, will always raise up some sincerely to devote themselves to his service. We ought to remember that this seed, in which the service of God was to be preserved, is the fruit of the incorruptible seed; for God begets and multiplies his Church only by means of his word.
He continues on verse 31 (“They shall come, and shall declare his righteousness to a people that shall be born, because he hath done it”):
The Psalmist here confirms what I have previously stated, that since the fathers will transmit the knowledge of this benefit to their children, as it were from hand to hand, the name of God will be always renowned. From this we may also deduce the additional truth, that it is by the preaching of the grace of God alone that the Church is kept from perishing.