I still have a question regarding Satan. If he was in heaven he must have believed in God. He was a guard of God’s throne. He must have at one time loved God. He let the sin of pride creep into him. Isn’t this an early and prime example of how one could lose his or her salvation by turning against God and letting sin take over in one’s life. If you follow the OSAS theology you would have to say that Satan was not really saved or believed in God to begin with. The bible is very clear that Satan will be thrown into the lake of fire.
The doctrine of Eternal Security (OSAS) is unique to the Church. It does not apply to angels, it didn’t apply in the Old Testament, and it will not apply after the rapture. But speaking to the Church Paul wrote,
Now it is God who makes both us and you stand firm in Christ. He anointed us, set his seal of ownership on us, and put his Spirit in our hearts as a deposit, guaranteeing what is to come. ( 2 Cor. 1:21-22)
At the moment of our salvation, God accepted responsibility for us by putting His seal of ownership upon us and sealing his Spirit in our heart. He did this to guarantee our place in His kingdom. No other group had been or will be blessed in this way.
For more detail on the nature of post rapture salvation, click here.