Acts 16:31 says: "Believe on the Lord Jesus Christ, and thou shalt be saved..." Notice again that it doesn't say, "Believe and you will someday be saved." It rather says, "Believe...and BE saved."
The "Once Saved, Always Saved" doctrine is fundamentally flawed. The perfect example of how this doctrine is false is Judas Iscariot. He believed in Jesus Christ, walked with Him, was one of the Twelve and was given the same powers from Him as the others. Yet what Christian believes that Judas Iscariot went to Heaven?
How can we be assured of our own salvation if St. Paul wasn't (1 Corinthians 9:27)? Salvation is not a "one time" event, but an ongoing process until "the end" (Matthew 10:22; 24:13; Mark 13:13).
The Catechism of the Catholic Church addresses the issue of Salvation.
161. "Believing in Jesus Christ and in the One who sent him for our salvation is necessary for obtaining that salvation. [Cf. Mk 16:16 ; Jn 3:36 ; Jn 6:40 ; et al.] 'Since 'without faith it is impossible to please (God)' and to attain to the fellowship of his sons, therefore without faith no one has ever attained justification, nor will anyone obtain eternal life 'But he who endures to the end.'']"
162. "Faith is an entirely free gift that God makes to man. We can lose this priceless gift, as St. Paul indicated to St. Timothy: 'Wage the good warfare, holding faith and a good conscience. By rejecting conscience, certain persons have made shipwreck of their faith.' [1 Tim 1:18-19 .] To live, grow and persevere in the faith until the end we must nourish it with the word of God; we must beg the Lord to increase our faith; [Cf. Mk 9:24 ; Lk 17:5 ; Lk 22:32.] it must be 'working through charity,' abounding in hope, and rooted in the faith of the Church. [Gal 5:6 ; Rom 15:13 ; cf. Jam 2:14-26.]"
If you are trapped in a works based theology it is hard to understand. Judas lacked FAITH.
The Catechism of the Catholic Church addresses the issue of Salvation.
Just as the catechism also states:
424 Moved by the grace of the Holy Spirit and drawn by the Father, we believe in Jesus and confess: 'You are the Christ, the Son of the living God. On the rock of this faith confessed by St. Peter, Christ built his Church.
Sanctifiction is a continuing process. God the Father creating the human spirit is a one time event. Our rebirth by His creation of our new life is a one time event. Our renewing of our mind in a continuing process becasue our body and soul has been scarred from a previous lifetime as the natural or old man.
I agree with you that we continue to 'work' our salvation by remaining in fellowship with Him, where God does all the work in us, LOGOS to human spirit, human spirit to Mind (soul, NOUS portion), Mind to Heart (GNOSIS to EPIGNOSIS from NOUS part of our soul to the KARDIA part of our soul), then EPIGNOSIS categorizzed in our heart ready for us to exercise our volition and choose to remain in fellowship with Him and abide by His will. When we abide by Him in our volition using the tools now placed in our heart by the Holy Spirit, we become doers of the Word and produce good works per His plan, thereby working our salvation.
Our eternal life, though was created by an act of God in an instant, just as in the future we will be caught up with Him in a twinkling of an eye.
Yes, I would agree the doctrine of OSAS is fundamentally flawed. That is why I don't believe it. Instead I believe that God gives us grace and God continues to guide us until we are glorified. It isn't our work that drives us home but the work of Christ and it is His continuing work that sanctify us. We could technically lose our salvation but Christ promises that He won't let that happen. We persevere because of Christ, not because of our actions.
As far as Judas Iscariot, Christ choose those who He will. He chose Judas for a particular mission. God could have granted Judas faith. He didn't.