Wikipedia – “Jewish eschatology”
The Midrash comments:
“Six eons for going in and coming out, for war and peace. The seventh eon is entirely Shabbat and rest for life everlasting”.
The Zohar explains:
[which has the numerical value of six]
Elaborating on this theme are numerous early and late Jewish scholars, including the Ramban, Isaac Abrabanel, Abraham Ibn Ezra, Rabbeinu Bachya, the Vilna Gaon, the Lubavitcher Rebbe, the Ramchal, Aryeh Kaplan, and Rebbetzin Esther Jungreis.