In Romans 4:12, 16-17a, we are told that we need to have the faith of Abraham. Without such faith is impossible to please Him (Hebrews 11:6).
Paul, then provides an illustration of Abraham’s faith (Romans 4:17-22). When Abraham’s having a child through Sarah, by strictly natural means was impossible (Genesis 17:17; 18:11) – when Sarah was barren, dead in the womb (Romans 4:19), ceased after the manner of women (Genesis 18:11) – he (after the initial shock) trusted God in this matter. Moreover, ultimately he gave God the glory (For he knew that such was not possible without God). M.C. Moser remarked, “It is easy to miss the chief points in Abraham’s faith. His faith was the result of two factors, namely Abraham`s deep awareness of his and Sarah`s physical impotence, and the power of God to fulfill His promise to give them a son… If they had been blessed with normal bodies, having a son would have required neither divine intervention, nor such faith as Abraham had” ( The Gist Of Romans, p. 36).
Question: Since this child (Isaac) came miraculously as a gift, by the grace of God, does this mean that there was no human activity necessary to secure this promise? No, it does not. There is no evidence that Isaac was conceived without Abraham’s “knowing” his wife. To the contrary, this child was of Abraham (Genesis 12:7; 15:3-4; 26:1-4; Romans 4:18; cf. Hebrews 11:12). This was not a “virgin birth.”
What’s the point? I believe that Paul wanted them (the saints to whom he wrote), and us to appreciate the fact that, though there may be human conditions to be met, the basis of salvation – is like that of Abraham and Sarah’s having a child in old age – both rest as a possibility in God, not man. Man is as much without strength to save himself without God’s help, as Abraham and Sarah were to bring forth a child! K.C. Moser has written, “Now, note the sinner. He too is ‘dead.’ But in sin. He is as helpless and hopeless as Abraham was…This both happened and was written ‘for our sake'” ( The Gist Of Romans, pp.38-39).
Now turn to Romans 5:6. We were without strength (helpless – NASB). I believe this connects back with Romans 4:18-20. but in due time (Galatians 4:4; Ephesians 1:10; cf. Romans 5:6) – Christ died for us!
Human conditions? Certainly, there are human conditions for salvation. However, such is not even under consideration here. Instead, the point is to show us that without God’s intervention, our salvation would have been just as impossible as Abraham and Sarah having a child in the state in which they are described.