What does "Keep the Commandments" mean?

If Christ "fulfilled the law," and Christians no longer follow the law of Moses (e.g., circumcision is no longer necessary for membership in the kingdom, we eat pork, we pick up sticks on the sabbath, we don't raise up seed unto our brother, etc.), why do we still keep the Ten Commandments?

When we speak of keeping the commandments, why do we often cite the Ten, rather than the Two?

Or why don't we recite the Sermon on the Mount, for that matter?

(Side Note: I memorized the Sermon on the Mount when I was a teen-ager. I didn't stop to think that I couldn't do it because it was too long. I just memorized one verse at a time until I was done.)