What does Romans 4:17 mean?

Paul wrote at the end of the previous verse that Abraham is the father of all who share in his faith in God. Now, as evidence of this, Paul quotes what God said to Abraham in Genesis 17:5, "I have made you the father of many nations." These nations include all people whose faith is in God.

Paul then picks up the statement he'd begun just before this quote. Abraham is father of all believers in the sight of God. That is, Abraham is the spiritual father of all believers, not just of those who are under the law, meaning the Jews. Paul describes the God Abraham believed in using very specific terms. This is the God who gives life to the dead, partly referring to God bringing Abraham's and Sarah's bodies back to life-giving form even at the ages of 100 and 90 respectively, fulfilling His promise to give them a son. It is true, as well, however, that God also brings life to the dead in the sense of resurrection from the dead, as He did when raising Jesus back to life after the crucifixion.

This is also the God who calls into existence things that were not there before. Again, this likely refers to Abraham's and Sarah's promised miracle child and the nations that would come through him. Nations that had never been would spring into existence, including the nation of Israel.

It is also possible that Paul is describing God as creator of the universe, tying back to what he wrote about those who reject God in spite of witnessing all He has made (Romans 1:18-20). Those who believe in Him, as Abraham and all of his offspring do, understand and embrace the truth that God is the maker of all things. This is often described as creation ex nihilo, meaning "creation out of nothing."