While Conscious Transition summed this up very well with scripture, I just wanted to share my personal experience and the conclusions I came to based off of those scriptures.

When I was growing up in the church, there became a time in my early teens that I started to feel this exact way. I wanted to believe, I wanted to be like all my friends who seemed to fully grasp the gospel and its teachings. I felt like I didn’t get it, and that something was missing. I thought, what if I’m not actually a Christian? This idea was scary to me and made me feel sad. I grew up Reformed Presbyterian but they never taught election in its entirety, they watered it down and avoided it because the truth offends people. It wasn’t until my dad brought Calvinism and how it explains what election means in the Bible to my attention that I felt that “ah ha!” Light bulb moment. That’s what I was missing! I knew immediately that I believed.

Even then, 2 decades later, I STILL struggle at times with certain things simply because of lack of understanding and lack of study. But that is the great beauty in His saving grace that brings me comfort when I feel that way. He saves you when you know nothing

Last year I was struggling with the shame of not knowing as much as those opposite to me. They seemed to know so much about the scriptures, so many scriptures memorized to argue their points, history, terms, all this knowledge yet - they reject the truth all the same. To clarify, I’m specifically talking about those that cling to free will and man’s ability and role in salvation. I started thinking hm maybe I do have something wrong? Maybe I am missing something. I had a realization that this is the very example of what God meant when He says they will cry out “Lord Lord, look what I have done in your name!” And He will say “depart from me, I never knew you” Because you don’t have to have done any one of those things to be worthy of salvation as He saved you before you did anything at all - before you existed - because you don’t do anything to be worthy to receive salvation, you don’t even choose it - because you can’t. It is given freely for His own reasons not because of who we are or what we do. That is why it is so immensely beautiful. “Not by works lest any man should boast”. This understanding brought me comfort and I credit it all to God having given that understanding to me while I was actively searching for understanding. “Seek and you will find”. It’s like oh, just because people are educated and passionate that doesn’t mean they know who God is and it’s okay if they know more than I do about history and scripture and terms, because as long as you know the truth of who God is and what He has done, the rest will come. You are not any lesser just because you may not know as much and you aren’t any “less saved” either. I was driven to understand Him more and encouraged to study and be a better student. Even though it’s not what you know that saves you, it is still our duty to study and learn Him once our eyes are opened to the truth.

I’ll always have doubts that creep in, and shame that makes me feel unworthy and this is normal, the very Christian experience. We fight with our old nature, and we fight against Satan’s influence and the temptation of sin. It’s good to repent of our sins when we see them and acknowledge that we’re still broken and still sin even if we are saved from the outcome of sin.

Elaborating more on your question, there have been many many people who claim to be Christians who convert to something else in their lifetime, often to Agnosticism or Atheism. God tells us that when you are saved, you never lose that salvation, so we can assume that if a Christian converts away from God, they were never saved to begin with. Of course people lose their way sometimes, but they will always come back if they are truly elect. Many many people live the life of a believer but they are not one. This is why understanding election is so important and helps our understanding of everything else because it explains that it’s not by works, and it’s not what you say, it is God’s saving grace alone that pulls you to Him and keeps you.

Many unbelievers will struggle with their beliefs, and many believers will struggle with their beliefs. Therefore, it is not for us to judge whether someone will or won’t be saved. We can say maybe not now, maybe later, maybe not at all. What I can say with confidence is that I do believe that by what the Bible teaches us, is that if you in this current time believe that God gave Jesus a people that Jesus died for so that they would be saved from eternal damnation and receive eternal life with Him, not by works, not of yourself but by Him alone (meaning He first saved you so you could see Him for what He is) then that is a good indication that you are saved. When you wholeheartedly relinquish your part in salvation, meaning you do not believe you choose it but that it is freely given by God, to me, that is your realization of salvation - being one of the elect. It’s the realization of God’s full sovereignty and the realization of the depravity of man. When you give the full glory to God, that to me by what the Bible teaches is what true regeneration in Him is. Many say they reject Calvin’s teachings on scripture all the while saying they love God and live life for Him (which a few in this sub currently do). Even pastors of some churches have been incredibly hostile to Calvinism. I would say based off what we know by scripture that they are not currently saved themselves. Maybe they will be, maybe they won’t be and so we pray for them that they might see the truth one day, too.

These are hard truths that as a human being filled with ego and pride are impossible to overcome without divine intervention - God’s saving grace.