1Jo 5:13 These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
2Co 13:5 Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?
The Bible says that we can know that we are saved and it says that we should examine ourselves to see if we really have faith.
Today some denomination brand franchises present doctrine not so much as a teaching to help us become more like Jesus, but as a distinctive against some other group. One example is the division caused by one group that espouses what could be called "criteria salvation" and another group that espouses what is called "easy beliveism".
The EB group accuses the CS group of elevating some measurement standard of salvation to the point where there is a danger of works based salvation such as when a person believes that his membership in the right church or having the right kind of baptism gets him into heaven.
The CS group accuses the EB group of being so cavalier about salvation that people may mistakenly believe that they are going to heaven when they are not even saved.
Each group often takes a legitimate concern and draws it out of proportion so that in the end Christians get into disputes about word meanings and often lose sight that we are supposed to be occupied with becoming like Jesus.
One element often found in these disputes is the OSAS argument. I happen to believe that when a person is saved, he cannot lose his salvation. I think a Christian can have assurance of salvation, but I would not feel comfortable assuring someone that he is certainly saved because I cannot look into his heart.
The OSAS argument can engender vehement passions often because some people feel that others may be eternally harmed by it (one way or another). I feel that God's sovereignty is not so easily frustrated by doctrine which may not be exactly right.
I wouldn't want to engage in a discussion with someone who has a passion against OSAS, but with a person who intellectually set against it, I would ask them if it was possible to be saved and then become unsaved and subsequently become resaved, what would happen that would cause a person to become resaved? Would this constitute a some type of works based salvation?
I think that Satan's purposes are greatly served if he can occupy Christians with activities to keep them chasing after their salvation and distract them from growing in Christ.
I think the reason OSAS is not listed is that if one were to put in every doctrine that he would believe in, he might find that no one else was in total agreement. As a result, room is provided for respectful disagreement and even courteous and enthusiastic questioning.