The Rebbe's letters explaining the era of the redemption — the resurrection of the dead, the Beis HaMikdash, and who Moshiach is:
The resurrection of the dead. Techiyas HaMeisim must take place physically, not only spiritually, and the Rebbe explained its details and purpose (IK 200); he also discussed the World to Come and bodily resurrection (IK 209). Consolation after loss and resurrection both unfold in progressive spiritual stages (IK 170). According to the Rambam there are several levels of Gan Eden, some physical and some spiritual (IK 6357).
The world in the era of redemption. In the era of redemption, physical reality itself will openly reveal G-dliness (IK 6571).
Who is Moshiach. Moshiach must descend physically from King David, while his inner soul can be that of Moshe Rabbeinu (IK 6987).
The Beis HaMikdash. On the distinctions between the Mishkan and the Beis HaMikdash in Chassidus, see IK 7153; on the purpose of the Ark in the Beis HaMikdash according to the Rambam and Ramban, see IK 8829; on Temple offerings, see IK 172, 308, 163. Each Jew builds a spiritual sanctuary within himself (IK 515), and Chanukah's rededication of the Temple is a lesson in personal sanctity (IK 10618). On the restoration of the gifts to kohanim, see IK 7841.
See also: Moshiach and Geulah – Awaiting Moshiach; Moshiach and Geulah – Bringing the redemption.