If I accepted once saved always saved as a valid doctrine I would buy into the heresy of the United Pentacostals some of whom believe once saved you can never sin again and therefore all your carnal actions are not sinful. Once saved always saved removes taking personal responsibility for your actions and choices you make in life.
A true believer understands and hears the message of the Gospel and produces fruit as evidence.
And a true believer can stop producing fruit by becoming so enarmoured of this world that living an obedient life becomes inconvenient.
What is apostasy? It is a falling away from faith. Is it your contention that apostasy will not become an issue for real Christians? Based on OSAS apostasy can
never be a reality because once you are saved it is impossible to fall into apostasy.
Rev 2:5-7
5'Remember therefore from where you have fallen, and repent and do the deeds you did at first; or else I am coming to you, and will remove your lampstand out of its place-- unless you repent. 6'Yet this you do have, that you hate the deeds of the Nicolaitans, which I also hate. 7'He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes, I will grant to eat of the tree of life, which is in the Paradise of God.' NAS
Rev 2:15-17
16'Repent therefore; or else I am coming to you quickly, and I will make war against them with the sword of My mouth. 17'He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes, to him I will give some of the hidden manna, and I will give him a white stone, and a new name written on the stone which no one knows but he who receives it.' NAS
Rev 2:20-22
20'But I have this against you, that you tolerate the woman Jezebel, who calls herself a prophetess, and she teaches and leads My bond-servants astray, so that they commit acts of immorality and eat things sacrificed to idols. 21'And I gave her time to repent; and she does not want to repent of her immorality. 22'Behold, I will cast her upon a bed of sickness, and those who commit adultery with her into great tribulation, unless they repent of her deeds. NAS
Rev 3:2-3
3'Remember therefore what you have received and heard; and keep it, and repent. If therefore you will not wake up, I will come like a thief, and you will not know at what hour I will come upon you. NAS
Who is being called to repentance in the letters to the churches? Believers who have followed false teachers who teach false doctrine and have been overcome by the cares of this world.