My understanding is that there is salvation of the spirit, soul and body. When you are redeemed by the Lord you are purchased by Him. No one can change that. But just like Paul said in 1 Corinthians you can build with wood, hay and stubble, they will all be burned up and you will suffer loss.
You can be like Edom and Reuben who for a bowl of beans sold his birthright (or in Reuben's case a sinful indulgence). Or you can do something even worse which is to excommunicate a prophet of God. I think in this case you would have to be in a position of authority in the church. But I understand that this is what happened in Sardis, they booted out those that the Lord sent to speak to them, blotting their names out of the church's rolls and therefore the righteous judgement that as you have done it will be done to you, the Lord blots their name out of the book of life.
Now if you do this then you become Laodicea. The Lord is no longer in your midst as a church, He is outside knocking to be let in. That by definition is the apostasy, they have left the Lord Jesus and He is no longer lord of their church. If you decide that you are not going to be ruled by the word of God then you are the apostasy. Even then you can be saved, He is knocking, if you open the door to Him He will come in to you.
In the end it is up to the Lord at the judgement seat. If you suffer loss, if you receive a reward or if He says He never knew you.
The problem with OSAS is that it is a foolish doctrine. They tell you that you can never lose your salvation. So they point to instances in the Bible where someone does lose their salvation and they say "they were never saved in the first place". So that makes the whole thing idiotic. What I want to know is who is saved and who isn't? They didn't do anything to help me understand that. Instead we have the fruit of the Spirit and the works of the Flesh. We have lots of Biblical help in discerning those. There is nothing that says if this person prayed 20 years ago that somehow that annuls the works of the flesh today. That is how the Lord told us we would know who is saved and who isn't, by the fruit.
Now Satan can disguise himself as an angel of light. So there is a lot of deceit and deception, false prophets are hypocrites, they are putting on an act and playing a role. So it requires discernment and you must examine the person. But to make the job easier we know that the apostles who wrote the New Testament have been thoroughly examined and sealed their testimony with their blood.
OSAS is also foolish because you are not the Lord, you are not omniscient, you will never know who is saved and who isn't until we all appear before the judgement seat. We are never told to do that. We are told to work out our own salvation with fear and trembling. That is what the Bible says, not what OSAS says. To many that teach that doctrine you pray, your are forgiven, that is it. There is no "working it out" and there is no "fear and trembling". They are equating being justified as being saved. That is not wrong, Paul says that we are saved by grace and it is the free gift of God. So that is certainly salvation. It has nothing to do with our own work nor does it have anything to do with reward. But it is clear from Paul's word in Philippians that there is much more to salvation than what he was referring to in Ephesians.
If you take my analogy of the two quarterbacks, one is not condemned to hell because he never panned out as a first round draft pick and the other isn't saved from hell because he won 7 superbowls. The point is there is a promise when we are saved, an inheritance, a birthright. The promise is "Christ in us, the hope of glory". One of those quarterbacks received that promise (allegorically) and the other didn't. That hope of glory is also a part of our salvation. Now the person who is living in sin is not going to receive that part of salvation. I have no idea if they are going to hell or not, that is up to the Lord Jesus. But what I can easily see is which of those two quarterbacks received Christ as the hope of glory (again this is an analogy, not trying to refer to either of them as being saved or not).
