Isaiah 43:12

I have declared - I have announced or predicted future events; I have warned of danger; I have marked out the path of safety. He had thus shown that he was the true God (see the note at Isaiah 41:22).

And have saved - I have delivered the nation in former times of danger, and have thus shown that I would protect them.

And have showed - Hebrew, ‘Caused to hear.’ I have made known future events, and have thus showed that I was God.

When there was no strange god among you - Before the time when there was any idol in the nation, and when, therefore, it could not be pretended that deliverance was to be traced to anyone but to Yahweh. The word ‘god’ here is not in the original, but is properly supplied. The word זר zâr is evidently used instead of זר אל 'êl zâr, as in Psalms 44:20; Psalms 81:9. It denotes a god that is worshipped by foreigners. The sense is, that their former deliverance could in no sense be traced to any such foreign god.

Therefore, ye are my witnesses - You who have so often been defended; you who have the predictions respecting future events, can be appealed to as evidence that I am the only true God, able to deliver. The doctrine taught in this passage is, that God may appeal to his dealings with his people as a demonstration that he is the true God, and that he is faithful and able to deliver - an appeal which may be made to his church at large in view of its trials, persecutions, and deliverances; and to every one who is his true friend and worshipper.