John Calvin Commentary Isaiah 43:12

"I have declared, and I have saved, and I have showed; and there was no strange [god] among you: therefore ye are my witnesses, saith Jehovah, and I am God." — Isaiah 43:12 (ASV)

I have told and have saved. This verse is a type of recapitulation (ἀνακεφαλαίωσις) of the preceding one, because Jehovah again states that he foretold future events and that he had actually accomplished what he foretold. To tell relates to foreknowledge, and to save relates to power and goodness. In short, he means that he alone is God, who both knows and does all things. Although these things were spoken to the Jews, let us also recognize that they belong to us, for all the predictions that have come down to us should be regarded by us as many proofs of both the knowledge and the power of God, so that we may rely on him alone.

And there is no strange god among you. So that superstitions may be banished and he may be elevated to the throne of his heavenly doctrine, he again mentions that he displayed his power and gave signs of his grace, without being helped by anyone. Therefore, it follows that those who are not satisfied with him alone will be excessively ungrateful and wicked.

“At the time,” he says, “when you worshipped no strange god, I openly and publicly displayed my power; and therefore it is unlawful to bestow on false gods what belongs to me.”

Yet in these words he does not so much commend the piety or religion of the people as he excludes all external assistance. It is as if he had said that while the Jews knew no other God, the miracles performed by him were so numerous and so great that it was perfectly evident that only he is God.

At the same time, Isaiah remarks that our unbelief hinders God from displaying his power among us. Away, then, with all errors and all wavering and doubtful opinions about God, if we wish to experience his power! For if we turn our minds to superstitions or idols, we will undoubtedly render ourselves unworthy of his assistance and kindness.

You are therefore my witnesses. Finally, he again summons them as witnesses, accusing them of base and shameful ingratitude if they conceal what he had abundantly made known to them; for the greater and more numerous the testimonies by which he has manifested his power and might to us, the more we are bound to declare them to others.