Paul makes clear that after we have been saved, there is a continuing conflict between our wanting to walk in the flesh, (that wants us to live in sin)- and our desire to walk after the Holy Spirit that now dwells in us - and Paul warns that choosing to live in sins (works of the flesh), will keep us out of heaven:
Gal 5:16 ThisI 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 youin time past, that they which DO such things shall NOT inherit the kingdom of God.
Paul warns us over and over, that if we believers choose to walk after the flesh, we will die spiritually - but if we choose to walk after the spirit, we will have everlasting life:
Rom 8:5 For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit.
Rom 8:6 For to be carnally minded isDEATH, but to be spiritually minded isLIFE and peace.
Rom 8:7 Because the carnal mind isENMITY against God: for it is not subject to the law of God, neither indeed can be.
Rom 8:8 So then they that are in the flesh cannot please God.
Verse 8:7 Paul warns above, that having a carnal mind is ENMITY against God, meaning you actually become Gods ENEMY.
Jas 4:4 Ye adulterers and adulteresses, know ye not that the friendship of the world is ENMITY with God? whosoever therefore will be a FRIEND OF THE WORLD is the ENEMY of God.
Also, Paul warns the church at Corinth to make sure they aren’t reprobates.
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?
He warns that some of the church that think they’re in the faith can actually have become reprobates.
The word reprobates is ADOKIMOS in the Greek, which becomes important in the verse where Paul himself says he has to subjugate his flesh (the flesh is worldly desires to sin) daily, lest after preaching salvation to others, he end up a castaway.
1Co 9:27 But I keep under my body, and bring itinto subjection: lest that by any means, when I have preached to others, I myself should be a CASTAWAY.
The word castaway is also ADOKIMOS in the Greek - reprobate.
Paul said he would end up a reprobate if he didn’t subjugate his flesh with its sinful desires, daily.
Scripture clearly in fact shows that continuing to remain in Christ is conditional on us 1) continuing to walk in the light, as He is in the light, and 2) continuing to walk after the spirit, instead of after the flesh.
OSAS is not biblical.