Why should your eternity be determined by 1 life time?

I believe I have looked at Christianity and the concept of Heaven/Hell open mindedly. I tried to approach it without bias or judgment however there are just too many questions with too many answers that just make no sense to me and that I do not understand. Like why would your whole eternity (which is a long, long time) be judged by just a few years of being mortal on Earth? Aren't we supposed to change and evolve? How can we do that if after just 1 lifetime all the rest of our time is decided? Why would a loving, forgiving God condemn someone to eternal damnation for 1 mistake? And if we have eternity couldn't 1 lifetime be considered a mistake? Why wouldn't we have many life times? There is so much I just do not understand.

Why should your eternity be determined by 1 life time?
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7 mo
Thank you to everyone who commented. It is appreciated and I think about most of them. 😊
Why should your eternity be determined by 1 life time?
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