I don't want to debate on this belief because everyone has free will. Yet, the justification for this doctrine is very much questionable in that many scriptures do not support Once Saved Always Saved Doctrine and goes against the character of God.
There are many places that show one can lose their salvation or become disqualified:
1. Many of Jesus parable gives great examples of this(the branches, the sower of the seed, the talents, the five virgins)
2. The churches in Revelation (lukewarm, turned away from first love) The book of Revelation really
3. The disciples (Peter denied Jesus, Matt 10:33)
4. To the end (Matt 10:22;Acts 14:22,16;Rom 11:22,Rev 2:5,1Tim 4:1,2 Pet 2:20-22,Heb 12:15)
5. Paul (1 Cor 9:27,Phil 3:11-13)
Anyone who has ever heed the call of the Holy Spirit, Confessed, Believed, was baptized, and received the Holy Spirit inside them is or was saved according to scripture. They're name has been written in the book of life, but only those who are victorious until the END will not be blotted out(enter heaven). People can turn their backs on God, just as Satan and the angels did. The Spirit that living in the Saints is perfect, but the flesh is not. We can grieve and quench the Holy Spirit. Sin can not enter heaven there are no exceptions to this, because God doesn't dwell with iniquity or even listens to a person who has iniquity inside them. So if you have sin at the end and did not run your race, as always sin=death. No such thing as reborn or resaved, just repenting (turning from your sins back to God). That's why backsliders aren't rebaptized(or shouldn't be) because they have repented and turned back to God. They just start their race again.
I'm glad you believe in repentance because many OSAS don't. I was told I could murder and because of OSAS I could still go to heaven despite scripture saving I most certainly would not. I attended a Baptist church for years as a child. Not hounding, just showing opposing scripture to the OSAS doctrine.