God's Word definitely gives warnings about falling away
Yes, yes it does.
We can disqualify ourselves by turning away from the Lord to walk after the flesh which is going back under condemnation.
The OSAS people falsely claim that even if one is walking after the flesh (living in sin) they are still saved.... that's the false security in sin so called "gospel" that satan has brought in to the church as he teaches people to twist and reject God's Word just like he did with Adam and Eve in the garden of eden.
Ephesians 2:10
For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them.
Romans 8:1
There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
Romans 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.
(NOT in our own strength - see Philippians 4:13)
2 Peter 2:20
For if after they have escaped the pollution of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
Romans 6:14-16
For sin shall not have dominion over you: for ye are not under the law, but under grace.
What then? shall we sin, because we are not under the law, but under grace? God forbid.
Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
Now... watch them reply and say these passages are not for Christians are some other excuse to ignore God's warnings that they got from their father the devil.