Those who believe the power of God is unable to keep them saved, do not understand the true nature of salvation. I spent 10 years in the Assemblies of God, graduated with a BA in Bible from and A/G college, and later left the A/G due to doctrinal issues, one being the teaching that God’s grace and power were sufficient enough to save us, but not keep us. My Father loves me, He may discipline me, but He will never condemn me. I was born of my earthly father, and I can never cease being his son. I was born of my Heavenly Father, born from above, born again, and “nothing can separate me from His love.” He loves me, and He will keep me. Thank God, I no longer have to live my life in fear and wondering, did I cross the line? “Perfect love cast out fear.”
"Those who believe the power of God is unable to keep them saved, do not understand the true nature of salvation. "
That's not the point at all. I am convinced God could have kept Eve from sinning and that there would have never been a need for Christ to come for our Salvation. Did God do that? No, so supposing that because God is capable of a thing He will do that very thing is not relevant in the least. God gives us the free will to accept Salvation then to continue to believe and live as if we are believers. Those who don't are either once again in a fallen state or they're not, that's the issue.
Of course God has the power to save us and to keep us from falling but you can find plenty of folks in prison for murder who will tell you they were "born again" as a child and now don't believe in Christ because He let them fall. So, did God keep them from falling or did God allow them to be deceived into thinking they were saved when they were not? We have a role to play as well and the limits of our role is what is at issue when you talk about OSAS, not the limits of what God can do.