The ashes of the Parah Aduma when Moshiach comes and the Parah of Moshe Rabbeinu [including a fascinating discussion of who is greater - Moshaich or Moshe].
See how the Rebbe answers a professor who doubts the veracity of maamarei chazal [rach"l]. He read everything and knew how to answer. [See especially footnote 12.]
Halachos we keep today because moshiach might come ANY SECOND!