He said, Surely they are my people. Israel was first recognized as "a people" in Egypt, when the creel Pharaoh, probably Sethos I said, "The people of the children of Israel are more and mightier than we "(Exodus 1:9).
Soon afterwards God acknowledged them as "his people" (Exodus 3:7). The exiles probably go back in their thoughts to this time. Children that will not lie; or, deal falsely, as the same word is translated in Psalms 44:17.
The meaning is, that surely they will be faithful to God, and not fall away from him into idolatry or irreligion.