But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel, (ESV)
I love how Paul starts this verse. It is not as though the word of God has failed. There is a principle here that we need to hold on to in every situation of life. The word of God has never failed. The word of God never will fail. Our understanding is clouded by our finite understanding. The way that we see things is not always accurate. If our perception differs from what God's Word has said, we are wrong.
Paul is looking at the plight of many of his fellow Jews. It would be easy to see the rampant unbelief and rejection of their own Messiah and assume that God must have failed in what he said in His Word. That would be a human and natural perception. It would also be a wrong perception. The word of God has not failed.
In verse 4 and 5 Paul lists the great benefits and promises that God gave to the people of Israel. He speaks of: "the adoption, the glory, the covenants, the giving of the law, the worship, the promises, the patriarchs, and the Christ." Given all that the Jews had received how could it be that so many were lost in unbelief.
The answer to that question is found in the second part of this verse. Paul says that not all who are descended from Israel belong to Israel. That phrase is quite an indictment. He is saying that God kept his word. Many of the Jews did not. The ones who are truly Jews are ones who are more than physical descendants of Abraham. True Jews are those who have surrendered their heart to God.
There is a lesson for all of us here. Just being related to someone who loves God does not make you a believer. Receiving promises does not make you a believer. God keeps his word. You need to keep yours. Place your faith in the one who always keeps his word.