Presumption - The church is very presumptious. Each denomination tends to believe they have got it right, and goes around condemning the others over some point or other. I know how easy it is to focus on one issue and miss much more important ones. Paul was always very keen on being cautous, loving and supportive.
Therefore, my dear friends, as you have always obeyed—not only in my presence, but now much more in my absence—continue to work out your salvation with fear and trembling,
phil 2:12
There is a classic salvation question. If I was asked why should I be let into heaven? Because Jesus died for me, he washed me clean and I walk in his ways.
Now Jesus talks of people claiming miracle powers, but he says go away from me evil doers. I know of "christians" who have convinced themselves to do terrible things against an "evil" enemy, yet they think they are walking in the Lord.
So I think OSAS is more about appeasing wavering hearts who want a label rather than discovering Jesus and his gospel for real. The problem is tribalism which Catholics and most religious groups use for their benefit, not because this is anything from the Lord, but it helps to make the enemies over there and we are all ok over here.
Now we know this is a lie, because Jesus himself says tares or weeds are sown amoungst the faithful, but to weed them out would cause too much damage to those young in faith, so you just have to walk faithfully. But those called to the Kingdom will never fail, or falter, because their calling is true, they are born from on high into eternity. So why do they need OSAS, because it is just a reality. But I think this is the point, you really do not know, but want a concept that gives you assurance, because you are not sure truly you have the Holy Spirit and need this idea to stay true.
For me, I have met so many off the wall christians in the "christian" church, I no longer think we have a clue how many really understand walking with the Lord and how many are along for the ride. But that is not our job, it is just to stay faithful.
So if you think I am against OSAS, I am not, I just think it is irrelevent.