When Moshiach comes.....

When Moshiach comes, the primary branch of Torah study will be the mystical dimension, which deals with knowledge of G-d's attributes and qualities.
And so if this is the case then how will we know how to observe the practical mitzvot?

Rabbi Shneur Zalman of Liadi explains that in the future there will be no lapses of memory. Once we learn something, it will be imprinted in our memory forever. Memory loss is a manifestation of impurity, which will evaporate when Moshiach comes. Furthermore, any memories that we might have lost before Moshiach comes will be restored to us. Therefore, we won't need to dedicate as much time to memorizing the details of the Law, and will be able to spend the bulk of our time studying the inner dimensions of Torah.

Additionally, in the Messianic era we will be granted an extra level of understanding and from our study of the Torah's mystical dimensions, we will be able to infer all the practical laws of Jewish observance.

The Lubavitcher Rebbe adds that when Moshiach will come our evil inclination will be removed, and our nature and instincts will be transformed. Just a a young child instinctively draws his hand away from fire, we will have a natural aversion to those things forbidden by the Torah, and a natural inclination to do the things the Torah requires.