Second, 'being cut off' has nothing to do with losing one's eternal salvation.
In the passage, the Jews are unsaved not saved who became unsaved.
It is speaking of God turning once again to focus on the Jew instead of the Gentile in giving the Gospel
You don't work to get saved and you don't work to stay saved.
If you don't keep the Commandments, Bud, you can't make it to Heaven, the Bible is clear on that.
James 2:20-24: 20You foolish man, do you want evidence that faith without deeds is useless? 21Was not our ancestor Abraham considered righteous for what he did when he offered his son Isaac on the altar? 22You see that his faith and his actions were working together, and his faith was made complete by what he did. 23And the scripture was fulfilled that says, "Abraham believed God, and it was credited to him as righteousness," and he was called God's friend. 24You see that a person is justified by what he does and not by faith alone.