The Levitical priesthood was only necessary for a period of time until the Melchizedekian priesthood was fulfilled in Christ.  The lesser priesthood (and the lesser covenant) are no longer needed! Why have the Mosaic Law at all?!?

With all of the calendar changes, wars, natural disasters, and other events, we don't know what day "the seventh day" really is.  We are free to observe whatever day we want.

The physical law (the commandments of the Mosaic Law) was given to physical Israel but we are spiritual Israel so the physical law doesn't apply to us.

Afterward all the sons of Israel came near, and he commanded them to do everything that the LORD had spoken to him on Mount Sinai.  (Exodus 34:32)

The Law of Moses was given to the Jews at Mt. Sinai.  I am not a Jew therefore the Law does not apply to me. 

Moses went up to God, and the LORD called to him from the mountain, saying, "Thus you shall say to the house of Jacob and tell the sons of Israel..." (Exodus 19:3)

Trying to apply the law of Moses to Gentiles would violate the letter of the law itself since it is addressed only to the Jews at Mt. Sinai and their descendants.