The Future Beis Hamikdash Will Also Be Built With Iron

The first and second Batei Mikdash were destroyed by iron, so iron is excluded from those Batei Mikdash.

The future (third) Beis Hamikdash, an eternal house that will not be destroyed, has no need to worry about iron, since in the future the negative aspect of iron will be abolished.

The Beis Hamikdash of Moshiach will be built also with iron, to emphasize the elevation of the iron that destroyed the Beis Hamikdash into iron in its construction.

The quantity of iron will be abundant: one hundred thousand Kikarim in the building itself.

(The Rebbe King Moshiach Shlita, Vayechi 5752)