First, please capitalize God next time. Secondly, God made us perfect in his image, but because of the fall of Adam and Eve they have brought sin and diseases in our world. So you should not get body modifications for fun or just because, you can if necessary.

some denomination of Christians do get a small tattoo on their hand when they become clergy

Yes, Coptic (although they’re not all completely Christian).

Also, that 1 Corinthians passage may apply here, but in the context I think it was speaking more specifically towards sexual sins.

Yea kind actions should, just because you do one thing good doesnt mean you you can do another thing bad. Said Hindu might be doing things better than said Christian, but is the Hindu Christian? No, so he won’t go to heaven, neither will said Christian go to heaven if he did terrible things. Also please capitalize God next time.

No, literally every major religion is mutually exclusive. Just as one example, Surah 4:157-158 in the Quran says that Jesus was not crucified, while obviously Christianity disagrees. Was Jesus God? Christianity says yes, but Orthodox Judaism says no. Are the Vedas authoritative religious texts that we should all follow? Many Hindus would say yes, but Buddhism began in large part as a rejection of the Vedas. The list of mutually exclusive religious truth claims goes on and on. If God exists, by definition he has revealed himself through one religion, not all of them.

Additionally, you can’t get to heaven by being a good person. Any “god” would have to be perfect, or they wouldn’t be a god. And you can’t work hard enough to get to heaven because it’s not possible to become perfect. You must be perfect to be in heaven. This is why Jesus had to come to pay for our sin himself, because we couldn't do it on our own. It’s literally impossible. The prophet Isaiah makes it crystal clear: we are unclean and our righteous works are like filthy rags (literally translated, it means a menstrual rag) to God (Isaiah 64:6). As does Paul in his letter to the Romans, “All have turned aside…no one does good, not even one” (Romans 3:12).

(Also, this is why other religions than Christianity are false. They all say you have to work for your salvation. In reality, if salvation means you are spending eternity with a perfect God (which by definition cannot tolerate imperfection), then you either have to become perfect, or that god is not perfect. The first is impossible, the second means that’s not a god, and therefore a false religion. There’s a lot of other reasons which I can explain, but that’s just one.)

I disagree with Syl a little bit here. Orthodox Christians tend to, I would say, overemphasize the works that you have to do and the rites and rituals that you have to follow. In reality, Jesus has done all the work and all you have to do is trust him. Christians do act in love and kindness and do “good deeds”, but not to earn salvation. We do it because we love God for saving us and want to do what he says (which is to love people).