"Always be joyous, for sadness is a great obstacle in serving God. Even if you sin... do not let it stop you from serving God. Limit your feelings of sadness and regret to the particular trangression you have committed, and then return to rejoice in the blessed Creator.
"After all, you have repented, and have no intention of returning to this foolishness again.
"And even if you know that you are not fulfilling every aspect of a particular mitzvah, do not lest this upset you; rather, think of the blessed Creator --- He knows that you want to serve him in the best possible way, but that you cannot do so at this moment.
"And when you perform an incomplete mitzvah, pay no attention to the evil inclination that wants you to stop carrying out this deed. Rather, say to it, 'In performing this mitzvah it is not my intention to anger God, nor am I carrying it out for my own honor'"
Rebbe Dov Baer of Mezeritch, Hayim V'Hesed # 3