Let all your deeds be for the sake of heaven. (Avot 2:12)

If a person wishes to accept completely the yoke of the kingship of Heaven, let him turn his mind away from any bad or worldly thoughts, fantasies or mediations. Even when he has his meal, let him set his mind on the thought that it is in order that he may be strong for the service of the blessed G‑d. It is necessary to make his spiritual pleasure greater than his physical pleasure, and as a result he will gain greater strength from the spiritual content of the food. This is the esoteric meaning of the verse, "How fair and how pleasant you are, O love, amid delights" (Songs 7:7): that you should have a love [of G‑d] amid your delights and pleasures. [Tzof'nat Pa'ane-ah (5)]

A man must therefore utter all his words for the sake of Heaven….

I heard in the name of the Baal Shem Tov: Why is the Shechinah in exile? Because "by the word of the L-rd the heavens were made" (Psalms 33:6) and a man must therefore utter all his words for the sake of Heaven, so as to draw the flow of the benevolent divine influence from this [creative divine] word of the heavenly realm to all the [lower] worlds. Nowadays, however, for our sins, all our talk is for the sake of physical desires and cravings. Even our words of prayer and Torah study are involved with alien thoughts and ulterior motives. Thus the [divine] utterance is in exile. [Kitvei Kodesh, 22b (5)]

It is written, "In all your ways, know Him". (Proverbs 3:6) This is a great principle…. In all his actions, even in ordinary, physical, material things that a man does, it is necessary that they should be a service, a worship for the need and purpose of Heaven alone, and without any other motivation. Even to the very slightest degree there should be no personal motivation, but all should be only for the sake of Heaven. [The Last Will of Rivash]

[Excerpted from The Baal Shem Tov on Pirkei Avot by Charles Wengrov (Institution for Mishnah Research)]