Likutei Moharan 35:4/ליקוטי מוהר"ן ל״ה:ד׳

14. Now, there are a number of aspects to sleep. There is physical sleep, which is a rest for the mentalities. And there is also an aspect of study which is likewise called sleep with regard to the cleaving <of the mentalities to> the Creator.

2This is the study of the Torah in its plain meaning. It is an aspect of sleep, as our Sages taught (Sanhedrin 24a): “He has made me dwell in darkness” (Lamentations 3:6) —this is the Babylonian Talmud. This is also the aspect of faith, as is written, “Your faithfulness in the nights” (Psalms 92:3) ; “and the darkness He called Night” (Genesis 1:5).

3Thus, when a person perpetually cleaves to the service of the Creator, so that as a result of this great cleaving his mentalities become overtaxed, he should then study the Torah in its plain meaning. For when he studies the Torah in its plain meaning, his mentalities/soul then enter into faith, in the aspect of “They are renewed every morning,” and they renew themselves and revitalize themselves from their exhaustion.

4This is the aspect of PaShTA, muNaCh, ZaRKa. The PShaTA (plain meaning) of the Torah, which is the aspect of “Your faithfulness in the nights,” is a NayCha (rest) for the mentalities, so that the mentalities are renewed as initially. This is ZaRKa —it was ZaRaK (thrown) to the place from which it was taken, <i.e., to Chokhmah>.