Better to enter life with one hand... is about oneself or a whole church?

Just a small nitpick with your statement nobody ever finds their hand causes them to sin? Umm do you want to rethink that? I can think of three ways you can sin with your hand and thats in the first five seconds of thinking. All three of them I cant really mention here because of the rules but I think you get what im talking about. I think thats what jesus was talking about. The lust of the eyes, inappropriate lustful things you can do with your hands (im sorry mods if thats going too far give me a warning and delete this if it is), these are grevious sins in the eyes of God and if you find that your quote on quote right eye is causing you to commit lust its "better" for you to pluck it out or if your hands are causing you to sin in this manner than its better to cut off your hands than to endure the terrible wrath of God which is real, terrible, and everlasting. Thats what Jesus was saying.

God knows your hand or eye literally can't operate on its own. This is where easy reading translations and others get really weird. The actual translation isn't "causing" you to sin. The word is skandalizō refers to something that repeatedly causes one to stumble into sin or leads toward spiritual ruin. So if you can't stop sinning with your hand, cut it off. That's not saying Jesus is literally telling you to cut it off, the point is how serious he is about sin. Same idea when Paul says we are supposed to kill our flesh. That doesn't mean we kill ourselves, it just means we are supposed to figuratively "kill" our desire to sin. So in essence, if you constantly look at women with lust, look at the floor when you walk by, close your eyes... do stuff that prevent you from leading yourself into sin. Don't make sin easy to walk into.

Other examples: If video games constantly cause you to sin "cut it off". Stop playing.
If music brings up bad thoughts towards others, cut it off. Stop listening.
If friends are persuading you to drink to get drunk and go out and do sinful stuff. Cut them off. Stop being their friend.

Drastic action.

What that passage means is that you want to be very sure about your salvation and take God and the Bible seriously. Almost like if cutting off your own arm was the only way to make sure you're saved, then that's what you would do.

Obviously it's not supposed to be taken literally and it's not about sin or turning from sin either, it's just simply saying that be serious about the things of God because we're alking about heaven and hell, and it ought to be taken very seriously.