Of course. If you are your father's son, nothing can change that. Similarly if one is a child of God nothing can change that, since no one can be "unborn". Even little children understand these elementary truths. A genuine Christian is a child of God, and therefore must live like one. If someone is not living soberly, righteously, and godly, then that person is NOT a child of God. He or she may claim to be "Christian" but that is self-deception.
Since OSAS has come up, let's call it a misnomer. The correct term is "the eternal security of the believer" (not the pretender). The Bible is very clear that every child of God is eternally secure in Christ. No one "loses" their salvation, since those who seem to do so were never saved to begin with. And Paul even called the carnal among the Corinthians "saints" (sanctified ones): Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called [to be] saints, with all that in every place call upon the name of Jesus Christ our Lord, both theirs and ours:
Just ignore "to be" which is in italics but not in the text. "Called saints" is what Paul said/
Yes, you are your father's son, but your father can disinherit you for lack of relationship or lifestyle choices. And when this happens, you can not truly say that your father recognized you as his son in the real sense of it. Or else, he would not have disinherited you.
Why should I ignore the words -to be? Is it because it does not give credence to your meaning.. Well, to me, whether we take it out or not, it means the same. It is noteworthy, Paul believed that though, these converts are sanctified in Christ Jesus. they are not automatically saints. Even, in situations where they are called saints, they are saints by faith. Sanctification is a process. Therefore, they have to live the life of saints to produce "saintly" fruits of good works. We see Paul praying for the saints in Colosse that they might be filled with the knowledge of his (God's) will in all wisdom and spiritual understanding. That they may walk worthy of the Lord unto all pleasing, being fruitful in all good works, and increasing in the knowledge of God , strengthened with all might according to his glorious power unto all patience, longsuffering with joyfulness etc . This is to enable and empower them live in the way and manner of saints.
He told the Roman " saints" -- if any of them has not the Spirit of Christ, he is none of his. Recall that these are the saints who are sanctified in Christ Jesus. Since they are Paul's converts, it would be assumed correctly that at the time they converted and, believed, they must have received the holy Spirit and sealed as well. But, here Paul is portraying the fact that it is possible not to continue to have this Spirit of Christ in them. They can be found wanting. The scripture says quench not the Spirit. Can you rightly say that Paul did not regard them as true believers in the first place as you seem to portray in your post?
He told the Colossians that Christ has reconciled them in the body of his flesh through death, to present them holy and unblamable and unreproveable in his sight -- if they continue in the faith grounded and settled and be not moved away from the hope of the gospel which they have heard and which was preached to every creature which is under heaven ----------do you notice that proviso"" if they continue ------ what does that tell you?
God's salvation for mankind is eternal and offers eternal security for all who do the will of the Father which is in heaven. Paul shows in his epistles and the scripture generally shows that a believer can loose his stand in God by his choice of deeds if he stops walking in the light of God until he changes his way and comes back to the light.