"Paul is presuming they are filled with the Holy Spirit and have been chosen of God. And so should we. People fall away but they were never saved to begin with."
Then why does he warn us, and them, so continually about falling away or being "cut off"?
Do you have a verse. I'm not Mr. Answerman but I can give it a good shot. I will say there are a handful of problematic verses on this side of the tracks but they are significantly fewer than on the other side. I know. I've been there and I'm parroting all the verses that have troubled me for 30+ years. I don't get an explanation of what it is to be sealed with the Holy Spirit, what a new heart and new spirit means, how a Christian is born again, or what it means to be a "slave to righteousness". I throw out literally hundreds of verses (like my tagline) and all I get is, "Well, it's a mystery." All I hear is that we have "free will" although the Bible really doesn't state that.
Here's another:
What is He guarding that you have entrusted (past tense) to Him?