Question:
Romans 11:20-25 seems to be saying that while we are “grafted in” to the root of the olive tree, (saved) by grace, we could be cut off if we do not “continue in His goodness” (verse 22) and abide in unbelief (verses 20 and 23).

However, Paul may not be talking about salvation in this passage, but I’m not sure what he is talking about. So if you could help me, it would be greatly appreciated.

Answer:
Romans 11:20-25:  

20  Well said. Because of unbelief they (Israel] were broken off, and you [Gentiles] stand by faith. Do not be haughty, but fear.

21  For if God did not spare the natural branches [Israel], He may not spare you [Gentiles] either.

22  Therefore consider the goodness and severity of God: on those who fell, severity; but toward you, goodness, if you continue in His goodness. Otherwise you also will be cut off.

23  And they [Israel] also, if they do not continue in unbelief, will be grafted in, for God is able to graft them in again.

24  For if you were cut out of the olive tree which is wild by nature, and were grafted contrary to nature into a cultivated olive tree, how much more will these, who are natural branches, be grafted into their own olive tree?

25  For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in.
This portion is talking about Jews [Israel] and Gentiles being grafted into a tree and being cut off of a tree. Throughout scripture the Lord worked with, and blessed nations as well as individuals. The Jewish nation was God’s chosen nation marked out for blessing. That does not mean that every Jew who ever lived was saved and is in heaven. Even in the Old Testament, each person was saved by faith just like we are today (Romans 2:28, 29; 4:1-3).
Romans 11:25 shows that this chapter is speaking about the Jewish nation and all the other races of Gentiles: The Jews were given the gospel message first, and even though some received it, most of them did not (John 1:11). Paul was then commissioned to spread the gospel to the Gentiles (Acts 18:4-6; Romans 11:13). That is when the Gentiles were grafted into the tree as a race, and concentration was placed on spreading the gospel to them.
Verses 23 and 24 show: that the Jewish people can still be saved today—even though the gospel is mainly preached to Gentiles! It has been that way ever since Paul was preaching and it will stay that way until “the fullness of the Gentiles [will] be come in,” which I believe will end at the rapture of the church, which could happen at any moment!
Then, the Jews as a nation will realize that they crucified their Messiah, who is Jesus. At that time “every eye shall see Him” (Revelation 1:7). “And one shall say unto Him, ‘What are these wounds in Thine hands?’ Then He shall answer, ‘Those with which I was wounded in the house of My friends. . . . and they shall look upon Me whom they have pierced,’ and they shall mourn for Him, as one mourneth for his only son” (Zechariah 13:6, 10). Then the Lord will bless Israel again throughout the 1,000 year reign of Christ over the whole earth.
So, I believe Romans 11 is speaking about nations of people, rather than individuals. Regarding the salvation of individuals: many verses show plainly that once a person completes the transaction with God–trusting Christ and His work of bearing God’s wrath for our sins on the cross of Calvary–at that moment they have passed from death unto life, and God does a mighty work in that person which can never be erased. They become a new creation of God (2 Corinthians 5:17), their old man is crucified (Romans 6:6), they have eternal life as a present possession (John 3:16), they are indwelt and sealed with the Holy Spirit (Ephesians 1:13), and they are “in Christ” instead of “in their sins.” None of those things can be undone or retracted by God. That is certainly something to praise Him for!