Likutei Moharan 59:3/ליקוטי מוהר"ן נ״ט:ג׳

13. This is likewise the aspect of keeping Shabbat. As is brought in the Zohar: “You shall keep My Sabbaths” (Leviticus 19:30)—“My Sabbaths” is a circle with a square inside it (Introduction, p. 5b) .

2A circle is the aforementioned aspect of the Throne of Glory, the aspect of “The throne had a [back] with a rounded top.” A square is mishpat, in the aspect of “It shall be square [and] doubled” (Exodus 28:16), which was said regarding the choshen mishpat (breastplate).

3During the week, the Divine Presence gathers up holy sparks, whereas on Shabbat she ceases. However, in the Future, all evil will be eliminated, in the aspect of “They will no longer follow the dictates of their evil hearts.” Then, it will be a time of perpetual Shabbat. The same is accomplished through the aforementioned circle and square. As explained above, through them evil is eliminated, [and] this brings about the aspect of “My Sabbaths,” the aspect of a circle and a square.