אַאַמוּ"ר כּוֹתֵב שֶׁשָּׁמַע בְּשֵׁם רַבֵּנוּ הַזָּקֵן

My revered father, the Rebbe [Rashab], writes1 that he heard it cited in the name of the Alter Rebbe 

שֶׁכָּל הַמְּחַבְּרִים עַד הַטַ"ז וְהַשַׁ"ךְ, וְהֵם בִּכְלָל, עָשׂוּ הַחִבּוּרִים שֶׁלָּהֶם בְּרוּחַ הַקּוֹדֶשׁ

that all the Torah authors until, and including, the authors of Turei Zahav and Sifsei Kohen, composed their works by ruach hakodesh, Divine inspiration.

וְעִנְיַן רוּחַ הַקּוֹדֶשׁ אִיתָא בְּקָרְבַּן הָעֵדָה סוֹף פֶּרֶק ג' דִּשְׁקָלִים

The author of Korban HaEdah, at the end of ch. 3 of Tractate Shekalim, explains ruach hakodesh 

שֶׁזֶּהוּ שֶׁמְּגַלִּים לוֹ רָזֵי תּוֹרָה, שֶׁזֶּהוּ מִבְּחִינַת הֶעְלֵם דְּחָכְמָה

as a revelation of the secrets of the Torah. This revelation comes to an individual at the [preconscious] level of thought which [in the language of the Kabbalah] is called he’elem deChochmah [lit., “the latent dimension of wisdom”].

Text and Translation courtesy of Sichos in English