You posed a really tough question. I believe it is easier to prove God’s existence and the evidence for Christianity, than to prove the condition of the heart, and the heart of believer at that too.
Got Questions has a beautiful response to a similar question:
I struggle with this question a lot too, thus accumulating bits and pieces of answers during every struggle. Then one day the Holy Spirit gave me an AHA moment, culminating all the answers into a simple analogy for me by pointing to my own marriage. So, when someone (from my discipleship ministry) comes with a question along this line, I would use this analogy as well.
Imagine you are wedded to a wonderful spouse and have the most beautiful of a loving relationship. This state of bliss is like when we receive Christ and restored the privilege to have an intimate loving relationship with Him. But the story is not done, you have to cultivate your relationship to sustain the intimacy. Most people can point to a parent who may not have divorced, but barely enduring a cold and stale relationship of 20-40 years. Anyway, intimacy is for another topic another time.
When You Love Her
My point here is when you love your spouse, you will not do things to hurt him/her that will steal his/her smile, even though the temptation to do so is very very real. You will exercise great self-control because you love him/her. Sometimes you fail, I did too, but you’ll feel bad and seek to reconcile. And my own wife has been so gracious to forgive me because she loves me a lot. Imagine a God who is love, and loves you with His endless capacity to do so.
When You DON’T Love Her
But the difference is, when I don’t love her, or decided to stop loving her (because agape-love is a decision and a verb right?), I would succumb to temptation that will hurt her, but instead of feeling bad, I’m unrepentant and continually chose to overindulge myself in my depravity. I may start with sneaking around in secret, and spiral into sinning blatantly with her full knowledge, and in my hardened heart and ego, I purposely go into a greater frenzy, even while my wife continues to convince me that she is willing to forgive and softly persuading me to come back
If I were to turn back at this point, she would gladly restore our relationship and forget all my past sins. In 1 John 1:9 If we confess our sins, He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. In fact, Got Question also has an article on this: https://www.gotquestions.org/Christian-sin.html
Not Turning Back
But imagine if I’m unrepentant, and told her I don’t love her anymore (“decided not to” to be precise), and I want a divorce. She would relent and not allow a divorce, but then I forced my hands on her to push through the divorce with my ever hardening heart. I would spit on her, mock her, continues reveling in my sin, and finally out of true love, she lets me go.
A Loving God
Just as God loves us so much to respect our decision if we don’t want to be with God. He won’t force us against our will. But if we reciprocate His love, He will gladly restore our standing like the prodigal son, because no one can be too far out of reach from God’s love (Rom 8:39).
Heaven and Hell
I’m a believer in Hell is simply a place devoid of God, and Heaven is a place brimming with His presence. (whatever happens inside or what it holds within, that’s for another doctrinal debate) Sometimes, we assume wrongly that everyone wants to go and be with God for eternity(Heaven) and that no one wants to separate themselves from God (Hell), and that it is unfair for God to put people in hell.
A Fair God
No, if we understand what heaven and hell is, then God will put everyone exactly where they want to be, a place with their true love, or away from whom they hate. Just as it says in Gen 18:25b NKJV “Shall not the Judge of all the earth do right?” No one can say they didn’t end up where they didn’t want to or don’t deserve to be there. If they are supposed to end up in Hell, then even if God were to have a last minute conversation with them, they will still reject God, like Stalin did, raising his fist one last time at God on his deathbed,as Ravi told it in his book “Can Man Live Without God”.
Bringing It Home
I guess I believe in a doctrine, where once saved forever saved, nothing we can do to earn it, not by works but by grace through faith. (Eph 2:8-9). There’s no offense bad enough we can commit that if we want to confess (in agreement with God that we are wrong and get right with Him as the 2nd Got Question article mentioned) that God cannot restore the relationship. But if we don’t want it (decide not to want it), God is too loving to force you to be in Heaven with Him for eternity. (It’s like forced into an unwanted non-divorce-able marriage to an obsessed individual you hate LOL)
Don’t get me wrong, knowing this doesn’t mean I stop struggling with this question in parallel to walking in my 11 year old marriage (barely a teenager LOL), continually finding myself working it out(just as Phi 2:12 working out your salvation) to cultivate its fruit that not only I but people around me can enjoy as well. (Psalm 1:3)
I hope you find this brief response helpful and quite cogent for you from all angles of perspective you may develop from your double-headed question. May God continue to shower His love and wisdom for you to better understand your personal struggles. Thanks for bringing this up. Please feel free to CMIIW.
Blessings in Christ,