You are not accurately presenting our position in your words above. We believe that salvation occurs EVERY SINGLE TIME the "Spirit presents man wiht Spirit inspired Word and Spirit empowered messengers" but NEVER saves anyone when the gospel comes "in word only" without "Spirit empowered messengers."
You reference 1 Thess. 1:4
For we know, brothers loved by God, that he has chosen you, 5 because our gospel came to you not simply with words, but also with power, with the Holy Spirit and with deep conviction. You know how we lived among you for your sake. 6 You became imitators of us and of the Lord; in spite of severe suffering, you welcomed the message with the joy given by the Holy Spirit.
You read something into this text that simply is not there. Yes, Paul acknowledges the power of the gospel which came to the Gentile congregation (Acts 28:28), people who were NOT thought of a being the 'elect' of God (as the Jews were), and that is exactly OUR VIEW. The the gospel comes in power...enabling POWER, which is being sent to the Gentiles at this time. That is how we know the Gentiles, like the Jews, were CHOSEN...because the gospel was sent to them too. "The gospel is the power of God unto salvation for those who believe...first to the JEW and then the GENTILE."
The Gentiles acceptance of the gospel proves that the gospel IS POWERFUL...as it even enables the dirty barbarians of that day to accept and follow Christ. But did EVERY gentile who heard the gospel come? No. Why?
1. Because the gospel is just not powerful enough to enable them.
2. Because they chose to trade the truth in for lies and reject it.
I choose #2. Calvinism chooses #1
You are assuming that every time the gospel is preached it is empowered by the Spirit.
And you are the assuming that every time God's inspired truth is preached is doesn't have enabling power. Which is worse? To assume God's words have power or to assume they don't?
There are only three way the truth doesn't have power:
1. People don't hear the truth because its not available. (Rm 10)
2. They don't hear/see the truth because its being blinded from them. (Hardening - a condition not from birth, but one we can "become" after much rebellion in the face of God's long-suffering) (Acts 28, Mk 4, Matt. 13, Rm 11)
3. People choose to trade the truth for lies...(self deceived), which will eventually lead to becoming more hardened (see #2).