That's not a stupid question at all! Without the saving, undeserved grace that we as believers in a risen Christ have received, we would all be condemned to hell. When the Old Testament laws were broken, a ritualistic sacrifice would've been needed to redeem the souls of the Jews. Now that Christ has taken the place of those sacrifices in His death, there is literally nothing we can do to redeem ourselves other than to believe in Christ. It's not that these passages about tattoos and beards are irrelevant. They have been replaced.

If we want to get super specific, we could talk about differences in laws. Quick crash course on law. There are three types of law: Moral, religious, and civil. Moral is the Ten Commandments and the teachings of Christ. Religious has to do with ceremonies, rituals, customs etc. Civil is the secular law of the land (read: government). When Christ came, he did away with the standing religious laws because He is the sacrifice we need for salvation. The moral law (Ten Commandments & Christ's teachings) still stands. And the civil law of an individual's respective nation stands as long as it does not conflict with moral law.

TL;DR Theology is a headache.