Adam Clarke on Psalms 44:20

If we have forgotten the name of our God - That name, יהוה Jehovah, by which the true God was particularly distinguished, and which implied the exclusion of all other objects of adoration.

Or stretched out our hands - Made supplication; offered prayer or adoration to any strange god - a god that we had not known, nor had been acknowledged by our fathers. It has already been remarked, that from the time of the Babylonish captivity the Jews never relapsed into idolatry. It was customary among the ancients, while praying, to stretch out their hands towards the heavens, or the image they were worshipping, as if they expected to receive the favor they were asking.