Duties of the Heart, Fifth Treatise on Devotion 3/חובות הלבבות·שער חמישי - שער ייחוד המעשה ג׳

1The deeds that are perfected by devoting them to G-d alone while performing them are the acts of service whereby one hopes to find favor with G-d. These deeds are all the visible mitzvot (commandments) of the physical limbs. For it is possible to perform them without intent for G-d, such as to do them in order to appear important in the eyes of others, or to hope for their honor and praise.

2But 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).