The reason is that there is no uttered word that does not have a “Voice.” Now, a profane Voice ascends on high and rouses that which is called Chol, Profane. When the Profane is roused on the holy Shabbat, it is a great denigration. He who does so “separates friends (Proverbs 6:28).” The Holy One, Blessed is He, and the Community of Israel ask, “Who is this who seeks to break up our union?” For the Supernal Holy One does not dwell amidst the profane. This matter contains a deep mystery. As the profane entity is aroused on high, it, as described in Parshat Parah, “It defiles the Sanctuary of God (Numbers 19:20).”

Now if this occurs because of an insignificant word, it would certainly occur in the case of a more serious deed, which defiles the upper and lower worlds.

“Thought about mundane matters is permitted (Shabbat 113b),” for a thought has no Voice. But should a person utter words of Torah, words of holiness, a Voice is produced. It rises up and rouses the holy entities.concerning this, it is written, “go forth, daughters of Zion (Song of Songs 3:11).” [Sod haShabbat, Section 16]