John Calvin on Isaiah 46:9

9. Remember the former things. This is an explanation of the preceding statement; for he expresses more fully what he formerly meant, that is, that God hath testified of himself by sufficiently numerous proofs, and hath shewed what is his nature and greatness; and that not merely for two or three days, or for a few years, but at all times; for he had continued his benefits, and had incessantly bestowed his grace upon them. Hence he infers that the manifestations of his divinity, being so clear, ought to prevent them from giving their hearts to another.

That I am God. In this passage the particle כי (ki) does not signify for, but that, and introduces a clause which explains what goes before. Besides, as we have formerly explained, God wishes not only that he may be acknowledged, but that he alone may be acknowledged; and therefore he wishes to be separated from all the gods which men have made for themselves, that we may fix our whole attention on him; because, if he admitted any companion, his throne would fall or shake; for either there is one God or there is none at all.