If your sons keep my covenant. We must remember, in the first place, that the covenant was perfectly gratuitous, so far as related to God's promise of sending a Saviour and Redeemer, because this stood connected with the original adoption of those to whom the promise was made, which was itself free. Indeed the treachery and rebellion of the nation did not prevent God from sending forth his Son, and this was a public proof that he was not influenced by the consideration of their good conduct. Hence Paul says (Rom. 3:3), "What if some did not believe? is therefore the truth of God of no effect?" intimating that God had not withdrawn his favour from the Jews, having chosen them freely of his grace. We know too, that notwithstanding their efforts, as if it had been of set purpose, to destroy the promises, God met their malicious opposition with displays of his marvellous love, made his truth and faithfulness to emerge in a most triumphant manner, and showed that he stood firm to his own purpose, independently of any merit of theirs. This may serve to show in what sense the covenant was not conditional; but as there were other things which were accessories to the covenant, a condition was appended, to the effect that God would bless them if they obeyed his commandments. The Jews, for declining from this obedience, were removed into exile.
God, on the one hand, took vengeance upon the people for their ingratitude, so as to show that the terms of the covenant did not run conditionally to no purpose; while on the other, at the coming of Christ there was a free performance of what had been freely promised, the crown being set upon Christ's head. The obedience which God demands is particularly stated to be the obedience of his covenant, to teach us that we must not serve him by human inventions, but confine ourselves within the prescription of his word.