After all, it's the same God. However there are several ways of dealing with this. Ceremonial commandments apply only to the Jews. They are part of the specific Mosaic covenant. These are thinsg like the kosher laws and circumcision.
Moral laws apply to everyone.
Most of the 10 commandments are part of the moral law, except for the commandment about the Sabbath. I believe most people who take this approach would say that the specific requirement to worship on the Sabbath is part of the ceremonial law, but a general obligation to worship regularly is part of the general moral law. Thus Christians are free to choose the specific time we worship. A more radical approach says that the Law as a whole is no longer binding. Instead, we are entirely under grace, and our behavior should be guided solely by love.