They have reference beyond the scope of the Old Covenant sacrificial system, harkening back to the Abrahamic Covenant, in which G-d promised the Jewish people a land permanently to call our own. They have eschatological significance, and thus have not been entirely fulfilled as yet. For example, Yom Kippur points forward to the final atonement of all Israel promised in Zech. 12 and Romans 11. At all times, but especially in the case of our observance.
Circumcision is rooted in the Abrahamic covenant, and is the central sign of our Jewish identities.
A Messianic Jew has the freedom in the Messiah to subject himself to any presently non-binding Old Covenant Law or principle. For example, the B'rit Hadasha appears to teach a relaxing of the Laws of Kashrut. A daily testimony to our people and the Body of Messiah that we take being Jewish seriously. A daily discipline with a natural spillover into other areas of our lives. A good health practice.