Musar zu Jeschijahu 64:5

The worst of all of them is for one to not be serving at all for the sake of divine service, but rather in order to deceive others and to gain money or honor. On this type of person it was said: "it would have been better had his placenta turned over his face (died in the womb)" (Yerushalmi Berachot 1:5). On such a person, the prophet said: "we are all as one unclean, and all our righteous deeds as like a discarded garment" (Yeshaya 64:5).

Therefore, the deeper and more diligently he delves in his thoughts into recognizing the lowliness of the physical and its pleasures, the easier it will be for him to purify his thoughts and heart so that he does not turn at all to the evil inclination in anything whatsoever. Rather, his physical deeds will be as one forced and not otherwise.

However, just like we have divided purity of thought into two divisions, namely, the bodily actions and the actions of Divine service, so too the in-depth contemplation necessary to acquire purity in them divides into two divisions.