I have been a Christian for about 40 some years and only in the last 10 years or so, I have been learning more about Calvinism after struggling with various issues that I could not understand. I used to be an Arminian but over the years, the more I studied, the more I understand God's plan of Salvation and the works of the Holy Spirit, I tend to agree with Calvinism.
One thing I have learned is that Calvinism is a doctrine. Its a teaching and nothing more than that. Only God through the Holy Spirit that saves the elect.
I had issues regarding Arminianism doctrines is that they focus on human mind more than the Holy Spirit. Remember a story about David and his son in 2 Samuel 12:14? "the LORD struck the child that Uriah's wife had borne to David, and he became ill." and died. What did David do in faith? Caused me to think about David's faith in God's Sovereign.
I remember reading John MacArthur's books regarding salvation and he said "reformed soteriology can account for the fact that fallen, sinful, guilty, depraved children who die with no spiritual merit, die with no religious merit, die with no moral merit of their own, can be welcomed by a holy God into eternal glory! Only pure, reformed theology can allow for that because only the purist theology believes that salvation is all by grace!
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Holy Spirit and GRACE. Not their own merit. If infants are saved when they die, by what means are they saved? How did they get saved?
Also the same of those who are retarded--mentally disabled in the same category as an infant would be, in the condition of not having a capability to understand matters of salvation--if they are saved when they die, by what means are they saved?
If we TRULY understand the sacrificial work of Jesus Christ, because that is the only means that anybody can be saved according to God's will. Christ through His death and resurrection, every legal hindrance has been met and satisfied. There is nothing that can keep me from the promise. Its not about thinking our way into salvation or to reason our way into salvation. The only way to get in is to believe Him with my heart which is sealed by the Holy Spirit through the gift of Faith, through Jesus Christ, His grace and the conviction of the Holy Spirit.
It took me YEARS to understand this. I hope this post will help but if not, I will do my best to keep posting and clarifying as I can. I would ask the Holy Spirit to help because it was the Holy Spirit that made me understand fully.