Do you think you can lose your salvation?
Yes, but I'm not quite as passionate about defending that particular doctrine as I am in my beliefs that are opposite of the first 4 doctrines of TULIP. While I believe it can happen, I also believe it's not something that can just happen easily.
But, I believe that God doesn't force us to keep our faith until the end. We are responsible to do that. Not without His help, but He does give us some responsibility in that. I don't think free will ends until we die. This is what the author of Hebrews said to his fellow believers:
Hebrews 3:12
See to it, brothers and sisters, that none of you has a sinful, unbelieving heart that turns away from the living God. 13 But
encourage one another daily, as long as it is called “Today,” so that none of you may be hardened by sin’s deceitfulness. 14 We have come to share in Christ,
if indeed we hold our original conviction firmly to the very end.
How does your doctrine make any sense of this? How can OSAS be true in light of a passage like this (there are others as well). Here is a warning given to believers about being careful not to be deceived and turn away from God. He wouldn't have warned them about that if it wasn't possible. Also, how can someone turn away from God if they aren't in a relationship with God in the first place?
In case you think he wasn't writing to believers here, look at how he referred to them earlier in the chapter.
Hebrews 3:1 Therefore,
holy brothers and sisters, who share in the heavenly calling, fix your thoughts on
Jesus, whom we acknowledge as our apostle and high priest.
If that isn't a description of true believers, I don't know what is. Also, he wouldn't tell them to "encourage one another daily" (verse 13) to help avoid being deceived if they weren't believers. That's not something that would be said to unbelievers.
Another way to look at this is based on what is said about people in the book of life in the book of Revelation.
Revelation 2:10 Do not be afraid of what you are about to suffer. I tell you, the devil will put some of you in prison to test you, and you will suffer persecution for ten days.
Be faithful, even to the point of death, and I will give you life as your victor’s crown.
Revelation 3:5
The one who is victorious will, like them, be dressed in white. I will never blot out the name of that person from the book of life, but will acknowledge that name before my Father and his angels.
Notice in Rev 3:5 that Jesus indicated that He will not blot out anyone's name from the book of life if they are victorious, which we can see from Rev 2:10 has to do with someone being faithful until their death.
So, it seems to me that this implies that it's possible for one's name to be blotted out of the book of life up until the point of death. That can be confirmed by looking at this verse:
Revelation 22:19 And
if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.