ייִדישער מחשבֿה אויף ירמיהו 17:10

But for the duties of the heart, there can be no hypocrisy, nor expectation of honor, respect, or praise on account of fulfilling them since other people cannot look into one's heart. Therefore one's intent in fulfilling them is automatically only to the Watcher, namely, the blessed Creator alone, as written "I, the L-rd, search the heart, examine the reins.." (Yirmiya 17:10), and "the hidden things belong to the L-rd our G-d" (Devarim 29:28).

Surely, regarding G-d, it is more fitting and more obligatory on us to adorn ourselves in His service in our inner thoughts, heart and limbs, since He watches them and contemplates them continuously and nothing can distract Him from some matter, as the verse says "I am the L-ord who searches the heart; I test the reins" (Yirmiya 17:10), and "the eyes of the L-ord are in every place, beholding the evil and the good" (Mishlei 15:3), and "the eyes of the L-ord, that run to and fro throughout the land" (Zecharya 4:10), and the verse says regarding the awe one should feel regarding the watching of the Creator "Be not rash with your mouth, and let not your heart be hasty to utter a word before G-d; for G-d is in heaven, and you are upon earth; therefore let your words be few" (Koheles 5:1), and "The L-ord looks down from heaven upon men" (Tehilim 14:2).

Among them, that our minds not muse on [doing] transgressions, nor desire them, nor resolve to do them and other similar things which are hidden in a man and observed by none but the Creator, as written "I the L-ord search the heart, I test the mind" (Jer. 17:10) and "the candle of G-d is the spirit of man, searching all the inner depths of the heart" (Prov. 20:27).