What was true if some of the Jews

Their unbelief did not make God’s faithfulness of no effect.

The concept here may be that the lack of trust of some of the Jews in the oracles, the Scriptures, that were entrusted to them, could not in any manner take away from the trustworthiness of the Scriptures.

When the Jews broke the faith, this did not mean the integrity of what God had given was harmed or changed in any manner.

The Jews were supposed to approach the Law with faith, thus learning to walk in righteousness before the Lord.

Instead, the Scripture took the place of the Lord, and the Jews served by the letter of what was written instead of looking to God continually for every aspect of life.

The same mistake has been made by Christians.

The grace of God is intended to lead the Christian to faith in God through the Lord Jesus, resulting in righteous behaviour. Instead the grace of God has been perverted into an excuse to break the moral commandments of the Lord.