Not so sure that Paul didn't claim that. And of course Jesus told the Father I have lost none that you have given me. He also said he was forgiving all sin past, present and future. How sad it must be to live a life in constant fear of being cast into the lake of fire. Lot of Bible references that caution us to fear not.
Romans 6 whole chapter
Romans 6:1-4 What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it? Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
Romans 6:12-18 Let not sin therefore reign in your mortal body, to make you obey its passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness. For sin will have no dominion over you, since you are not under law but under grace.
What then? Are we to sin because we are not under law but under grace? By no means! Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to death, or of obedience, which leads to righteousness? But thanks be to God, that you who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from sin, have become slaves of righteousness.
Romans 6:15-23 What then? Are we to sin because we are not under law but under grace? By no means! Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to death, or of obedience, which leads to righteousness? But thanks be to God, that you who were once slaves of sin have become obedient from the heart to the standard of teaching to which you were committed, and, having been set free from sin, have become slaves of righteousness. I am speaking in human terms, because of your natural limitations. For just as you once presented your members as slaves to impurity and to lawlessness leading to more lawlessness, so now present your members as slaves to righteousness leading to sanctification.
For when you were slaves of sin, you were free in regard to righteousness. But what fruit were you getting at that time from the things of which you are now ashamed? For the end of those things is death. But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.
"Not so sure that Paul didn't claim that."
That is absurd and frankly indicates ignorance. I am positive Paul didn't claim that but just the contrary, despite out-of-context wresting of Scripture. Some more teaching ion this:
For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live. For as many as are led by the Spirit of God, they are the sons of God. (Romans 8:13-14)
And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (Romans 8:17)
Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind, Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God. (1 Corinthians 6:9-10)
Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body. (1 Corinthians 6:18)
Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage. Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing. For I testify again to every man that is circumcised, that he is a debtor to do the whole law. Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. (Galatians 5:1-4)
Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God. (Galatians 5:19-21)
For this ye know, that no whoremonger, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and of God. (Ephesians 5:5)
Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck: (1 Timothy 1:19)
If we suffer, we shall also reign with him: if we deny him, he also will deny us: (2 Timothy 2:12)
I therefore so run, not as uncertainly; so fight I, not as one that beateth the air: But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway. (1 Corinthians 9:26-27)
And if Paul wrote Hebrews (which I have good reason to doubt)
But Christ as a son over his own house; whose house are we, if we hold fast the confidence and the rejoicing of the hope firm unto the end. (Hebrews 3:6) Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God. But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin. For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end; (Hebrews 3:12-14)
For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses’ law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. It is a fearful thing to fall into the hands of the living God. But call to remembrance the former days, in which, after ye were illuminated, ye endured a great fight of afflictions; (Hebrews 10:26-32)
For ye have need of patience, that, after ye have done the will of God, ye might receive the promise. For yet a little while, and he that shall come will come, and will not tarry. Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul. (Hebrews 10:36-39)
Actually, besides what I wrote to you before,
"God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; (Romans 3:25) But he that lacketh these things [virtue; knowledge; temperance; patience; godliness] is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins." (2 Peter 1:9)
If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. (1 John 1:8-9)
For a multitude of the people, even many of Ephraim, and Manasseh, Issachar, and Zebulun, had not cleansed themselves, yet did they eat the passover otherwise than it was written. But Hezekiah prayed for them, saying, The good Lord pardon every one (2 Chronicles 30:18)
But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness. (Romans 4:5)
Meaning that past sins are forgiven on Christ's expense, and present and future sins are not imputed to those of true contrite and repentant faith, and who thus contritely confess sins in repentance when convicted of sin, as David immediately did when fingered by Nathan.
And while this is what believers do when faced with their sins, yet there are multitudes occasions of iniquity, that we are not aware of, but since justification is by faith being imputed for righteousness, and not that of attaining to practical perfection, then all those who are effectual faith, which does confess sins when convicted of sin yet who are not aware of many (I dare say most) are yet "accepted in the Beloved" on His account.
However, to harden one's heart at reproof in rebellion is a mark of unbelief toward the Lord Christ, and to die in such is to forfeit what faith obtains, as shown and explained.