In the ‘excerpt’ below from Rudi Steenhuis he aptly answers the titled question from Scripture.

But first I want to contrast the Bible’s two distinct gospel programs of God; 1) “the gospel of the kingdom” for Israel and, 2) the Pauline grace gospel of the Gentile church called “the body of Christ.”

1. Recall that Jesus preached “the gospel of the kingdom” that is to literally come on earth as was long-promised to the Nation Israel.
2. Then Paul received from the ascended Lord Jesus Christ the new Gentile “gospel of the grace of God” and salvation for all mankind (Gentiles and Jews) totally apart from Israel’s Kingdom program “under the Law.” Paul’s “gospel of Christ” includes the believers salvation, the indwelling “Spirit of life” and their Rapture to dwell “eternal in the heavens.”

By these two different gospels we have God’s intended plan for recovering the whole ‘kosmos,’ which is the bible’s Greek word for the spiritual universe of the heaven and the earth (cf. Gen. 1:1. Eph. 1:10).

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- This below was taken from: https://thebigpictureask.blogspot.com/2022/02/was-paul-saved-into-kingdom-or-grace.html with emphasis added throughout -

So, our question remains if Paul was saved into the Kingdom or (into) the Grace program. Let me share with you my conviction of this interesting question. 

Paul was born in Tarsus, which gave him the privileged status of being a Roman citizen. Paul was also a Jew and a Pharisee, Philippians 3:4-5, like his father, Acts 23:6. Being a Pharisee and a religious zealot did not however mean that Paul was saved. We know this plainly since Paul, at this time, did not believe that Jesus was the Messiah and Son of God. His commitment to the traditions of men (Mark 7:1-13), his rebellion against the movement called, "The Way" (Act 9:2, Act 19:9, Act 24:14, Act 24:22), and his persecutions of the believers who followed Jesus was a clear indication of this!

Even on the road to Damascus, as a blasphemer and persecutor (1 Timothy 1:13), he was not yet saved, until that moment when he met Jesus in that bright encounter, or possibly a little later. After this event, we read how Paul believed, as he went into the synagogues preaching that Jesus was the Son of God, Acts 9:19-20.

So, now we need to pause here and consider. Paul was now saved. But what program was he saved into?

Well, an interesting point that needs attention is that the Grace program was NOT YET revealed at the time Paul was first converted! Paul had not yet departed into Arabia for 3-years (Galatians 1:17) where he received, not all, but the very beginnings of the grace revelation, progressively revealed.

This means that, at this time, Paul is saved into the Kingdom program. Right? Hmmm? It's hard to say? Either he is, and there is nothing more to say or prove, or, as my conviction leans more towards, that he isn't, because of another technicality that must be considered. What might that be? Let's read Jesus’ words in the following scripture;

Matthew 12:30-32 He that is not with me [Jesus] is against me; and he that gathereth not with me scattereth abroad. 31 Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: BUT the blasphemy against the Holy Ghost shall not be forgiven unto men. 32 And whosoever speaketh a word against the Son of man, it Shall Be Forgiven him: but whosoever speaketh against the Holy Ghost, It Shall Not Be Forgiven him, neither in this world, neither in the world to come. (See also Mark 3:28-29).

As this verse suggests, there is an Unforgiveable Sin. A sin that will not be pardoned by God. Blasphemy (sacrilege, irreverence, desecration, disrespect, cursing, impiety) towards the Holy Spirit was the end of the line and a death sentence for the Jews.

(Please note: This unforgiveable sin is not applicable to us of this age of grace! For more details and scriptural proof, see here).

To understand this, one must consider that the Jews;

1. throughout their history, rejected God, by rejecting and killing their prophets (1 Samuel 8:7, Proverbs 1:24-26, Matthew 21:34-36, Luke 13:34, Romans 11:2-3).
2. They then rejected Jesus, and killed ‘the Son of God’ (Matthew 27:17-21, Luke 19:14, Mark 15:13).
3. Lastly, the ‘rejected the Holy Spirit’ when they killed Stephen, (Acts 7:54-60). This was the last straw, proverbially speaking, and God blinded the Jews (Romans 11:25), and closed the Law Program, replacing it with grace through Christ, (as) revealed (to and) by the apostle Paul.

You see, Paul, like the Sanhedrin and those who threw the stones, was just as guilty of Stephen's death. Paul had committed the unforgiveable sin. He had blasphemed the Holy Spirit (Acts 7:55) … speaking through Stephen. It is my conviction that Paul was not saved into the Kingdom program when he met Jesus on the Damascus Road, even though he now preached that Jesus was “the Son of God.” Another thing to recognize is that Paul could not respond to faith in the Kingdom program because Paul had seen Jesus in his glorified state BEFORE he had the opportunity to confess Jesus as the Son of God. In other words, Paul could not confess Jesus as being God through faith anymore, because Paul has already seen Jesus as God on the Damascus Road. (Remember, faith is required for salvation, irrespective of which gospel was received).

This is contrasted by the order of events with Peter, James and John. In Matthew 16:13-17, Jesus was able to get the confession of faith from his (Messianic) disciples six days BEFORE He transfigured in front of their eyes (Matthew 17:1-2). Peter, James and John were able to act in faith by confessing Jesus as the Son of God before they actually saw Him in a measure of glory.

Paul was not able to be saved by the Kingdom gospel.

This leaves us with the Grace gospel. Do we have evidence that Paul was saved by this gospel? As a matter of fact, it is Paul himself which tells us precisely which program he was saved into. Let's see what the Bible says,

2 Timothy 4:17-18 Notwithstanding the Lord stood with me, and strengthened me; that by me the preaching might be fully known, and that all the Gentiles might hear: and I was delivered out of the mouth of the lion. 18 And the Lord shall deliver me from every evil work, and will preserve me unto his heavenly kingdom: to whom be glory for ever and ever. Amen.

The statement, "preserve me unto his heavenly kingdom", could not be clearer. It is difficult to say when Paul got saved? Did the Lord save him immediately on the road to Damascus into the Grace program? Did the Lord save him during his 3-years in Arabia? Did the Lord save him during his experience in the third heaven (2 Corinthians 12:2-3)? It is interesting that Paul used the word, "preserve", which gives the impression that the Lord kept him safe for a period before He saved Paul. Nevertheless, it is easy to say into which program Paul was saved. What is 100% clear is that Paul was saved into the Grace program because he mentions the "heavenly kingdom". The destination of “the Body of Christ” is of course the heavenly kingdom.

So, even though we have evidence by what we could extrapolate from the Bible about Paul not being saved in the Kingdom program, we can say without a doubt that Paul is saved by grace into the Grace program. In addition to this, I want to share one more scripture that seals the deal, so to speak. Paul wrote;

1 Timothy 1:15-16 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief [foremost]. 16 Howbeit for this cause I obtained mercy, that in me first*, Jesus Christ might shew forth all longsuffering (patience), for a pattern** to them which should hereafter believe on him to life everlasting.

* Paul was the "first"? The first of what?

The only sensible answer is ‘the first member of the Church, the Body of Christ’ (as the only other group of believers God has in His Word is the redeemed nation Israel, and Israel is (already) fallen at this point). Many have been saved before Paul, but he was the "first" to be saved in a new program/pattern of salvation by grace (no works). 

** Paul formed a ‘prototype’ of those who would follow him in salvation by the "pattern" Christ set in him. Those following being the Church, “the body of Christ,” saved by grace alone.

1 Corinthians 4:15 For though you might have ten thousand instructors in Christ, yet you do not have many fathers; for in Christ Jesus I [Paul] have begotten [created] you through the gospel.

1 Corinthians 3:10-11 According to the grace of God which was given to me, as a wise master builder I [Paul] have laid the foundation, and another builds on it.