4:17 as it is written. Again Paul appeals to Scripture (Gen. 17:5) for confirmation of his exposition. Rather than be father of Jews (the circumcised) only, it was already clear in Genesis that Abraham was to be the spiritual patriarch of all believers, Jew and Gentile alike. Nor is it unbelievable that the promise of God should be received by Gentiles also, for the one in whom Abraham believed “gives life to the dead.” This is evidenced in the new life that came from the apparently dead womb of Sarah (v. 19), in the life given back to Isaac when he was under the sentence of death (Gen. 22), and ultimately in the life restored in the resurrection of Christ (4:24, 25).
calls into existence the things that do not exist. This may refer to God’s creation of the world out of nothing (see Gen. 1; Is. 41:4; 48:13 for creation summoned into being by God’s word), or to the birth of Isaac (in which a nation emerges from a barren womb). Perhaps this also alludes to the words of Hos. 1:10; 2:23 (9:25, 26).