In Romans 8:13, IF is not a conditional, salvation maintenance program for believers but a confirmation of realm-diagnostic. Paul has already defined the 2 identities in verses. 8-11. Those in the flesh are unsaved, those in the Spirit have the Spirit dwelling in them.No. If is a condition particle. If Ye, you or I live after the flesh, ye, you or I will die. But if ye, you or I live after the Spirit and mortify the deeds of the Body ye, you and I shall live
He is speaking to everyone, everyone has a choice as to how they live and their choice through God's Spirit determines whether they live or die.
Couple that with the fact that the word therefore in verse 12 is a marker of an inference made on the basis of what precedes in verse 11. It is being said relation to the fact that He shall also quicken our mortal bodies if the Spirit dwells in us. Therefore, because of that we are debtors, under present obligation to live not according to the flesh. For if ye, you or I, live after the flesh ye, we, you or I will be about to die. But IF ye, you or I through the Spirit mortifying the deeds of the Body ye, you and I shall live.
Rom 8:3 For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh:
Rom 8:4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
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 is death; but to be spiritually minded is life and peace.
Rom 8:7 Because the carnal mind is enmity 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.
Rom 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
Rom 8:10 And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness.
Rom 8:11 But if the Spirit of him that raised up Jesus from the dead dwell in you, he that raised up Christ from the dead shall also quicken your mortal bodies by his Spirit that dwelleth in you.
Rom 8:12 Therefore, brethren, we are debtors, not to the flesh, to live after the flesh.
Rom 8:13 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.
The IF-clauses simply confirm which realm a person belongs to. They do not threaten Spirit-indwelt believers with spiritual death. You are reversing Paul's logic by making behavior determine identity, when Paul makes identity determine behavior.
The term "brethren" in scripture does not guarantee that every single person in a group of professing believers is a genuine believer. The apostle Paul does not infallibly know the condition of each person's heart, hence the warning.
The Apostle Paul specifically warns of "false brethren" (2 Corinthians 11:26; Galatians 2:4-5), indicating individuals who pretended to be part of the community but were not. Jude warned of certain men who have crept in unnoticed/ungodly men, who turn the grace of our God into licentiousness and deny the only Lord God and our Lord Jesus Christ. (Jude 1:4)
Judas Iscariot was a chosen disciple and part of the inner circle, but he is described as an unbelieving, unclean devil who betrayed Jesus. (John 6:64-71)
In the book of Hebrews, the writer warns the brethren against having "an evil heart of unbelief" (Hebrews 3:12-13), coming short by lacking faith in the gospel (Hebrews 4:1-3), showing that even those addressed as part of the group could lack true saving faith. Again, hence the warning.