For he said, Surely they are my people, children that will not lie: so he was their Saviour.
For he said, Surely they are my people. "He" - Yahweh "said," i:e., thought, in choosing them as His covenant-people; so "said," Psalms 95:10. Not that God was ignorant that the Jews would not keep faith with Him; but God is here represented according to human modes of thought, as saying within Himself what He might naturally have expected as the result of His goodness to the Jews; thus the enormity of their unnatural perversity is the more vividly set forth.
Children (that) will not lie - prove false to me, and my covenant (cf. Psalms 44:17).
So he was their Saviour - in virtue of His having chosen them as "His people." He became their Saviour. So the "therefore" (Jeremiah 31:3). His eternal choice is the ground of His actually saving men (Ephesians 1:3-4).