I was raised in an extremely strict religious family. I spent the majority of my life praising God, and going to church. I missed my entire childhood because of it. I didn't go to school dances, I couldn't play sports, I wasn't allowed to date until my mid-20's, I couldn't have friends outside of the religion. Now that I've escaped that environment, do you really expect me to have a desire to return to organized religion? Yes, I understand that most religions are much less time-consuming and strict. But that does not change the fact that I want to live my life to the most, now. I've already missed so much, and I'm not going to let life slip away again.
As you've mentioned, most religions aren't that strict. I wake up 15 minutes earlier than usual to read the Bible. I lose nothing from my social life due to that. I go to Church every Sunday. For an hour. And I also do some mission work, but a few friends I have do it with me so that's actually fun. I'm a 3 sport athlete (high school), and I have no clue what religion would keep you from playing sports.
Living the real "christian life" does not just imply being kind to everyone and donating to charity. It also implies spending precious time going to church and studying the bible, as well as giving up some things in your life (for me, one of those things would be homosexuality, a core part of who I am, as I am bisexual).
God loves you no matter who you are, bisexual, homosexual, or heterosexual. Being any of those does not restrict you from heaven (according to my religion, anyway). And as said before, waking up 15 minutes earlier won't kill somebody, nor will going to church for an hour a week. And if you say doing mission work is "wasting precious time," you have no idea how wrong you are. Knowing you are doing something to help people in need is one of the best feelings possible.
By assuming that you have an infinite amount of time, I strongly believe that you will never appreciate life like I do. I know this because I have never appreciated life more than I do now, now that I know that time is short and life is precious. We are not as special as we think we are. What makes us so great, that we deserve an infinity of time in heaven? We are heavily flawed biological machines, lucky to live 70 years. To me, that's not something to be depressed over, it's something to feel humbled and honored by: something to celebrate. I'm grateful to have this tiny snippet in time, and I'm not going to waste it on delusions that maybe I'll have more time than I actually do.
I agree that time is short and life is precious on Earth. I also think that when I DO die, I get to go to a better place. That gives me something to look forward to, but it doesn't make me view life as something bad. Celebrating life IS the essence of religion.
As a side note, the mere fact that I can be sent to "hell" for not believing in a deity who demands unquestioning faith in his impossible-to-prove existence turns me away from Christianity. In my humble opinion, that is not a God of love, that is a God of insecurity and power-hunger.
God is loving, gracious, and merciful, yes. But he is also holy, JUST, and hateful of sinners. Humankind is sinful. That's a fact; nobody except for Jesus is, was, or will be without sin. Except Jesus died for us on the cross FOR these sins, allowing us into heaven. If you believe Jesus did so, you're saved and will enter heaven. If you don't, then your sins are not forgiven, and you go to hell. So yes, you go to hell for not believing, but there's a reason for that: your sins weren't forgiven.
But that's only Christianity, so I can't speak for other religions
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I hope that clears up some misconceptions you seem to have about Christianity, or most forms of Christianity at least.