How sin can negate eternal life, per Paul:
In
1 Corinthians 15, Paul says they had heard him preach the gospel, had received it, and stand in it, and they are saved:
1Co 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you,
which also ye have received, and wherein ye stand;
1Co 15:2 By which also ye are saved,
If that’s all you read, you’d say it’s a done deal - they heard the gospel, they received it, stand in it, and are saved.
EXCEPT...
Paul’s next words make their salvation conditional, by warning them that though they’d heard the gospel, received it, stand in it, and ARE SAVED,
that they can end up believing IN VAIN, ifthey don’t keep in mind all that he taught them:
1Co 15:1 Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
1Co 15:2 By which also ye are saved, IFye keep in memory what I preached unto you,
unless ye have BELIEVED IN VAIN.
What was it that Paul taught them that they had to keep in memory that he had preached to them, that can affect their salvation, and cause their receiving the gospel, standing in it, and being saved, to be IN VAIN?
He taught them that he has to control and subjugate his flesh daily,
lest after preaching to others, he himself would end up a CASTAWAY - adokimos in the Greek. - a reprobate (rejected by God as one that failed the test).
1Co 9:27 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.
By subjugation of his body, Paul refers to the flesh, the fleshly desire to sin, i e, commit works of the flesh, as seen in another of Paul’s warnings to the saints, to the brethren against being DECEIVED:
Gal 5:16 This - I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
Gal 5:17 For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
Gal 5:18 But IF ye be led of the Spirit, ye are not under the law.
Gal 5:19 Now the WORKS OF THE FLESH are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
Gal 5:20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
Gal 5:21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell YOU again, as I have also told YOU in time past, that they which DO such things shall NOT inherit the kingdom of God.
Besides the “castaway” verse about becoming a reprobate himself,
He also warned the brethren to examine themselves to see if they were still in the faith, or had become reprobate (ADOKIMOS).
2Co 13:5 Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?