Musar su Proverbi 23:26

The heart is the king and mover of all other parts of the body and the leader over all of them. If the heart does not bring itself to serve Him, blessed be He, the service of the other limbs are worth nothing. For wherever the spirit of the heart goes, they will follow along as scripture states explicitly: "Give your heart to Me my son"(Mishlei 23:26).

One of the means which lead a person to acquire this trait is to prepare oneself for Divine service and mitzvot, namely, to not enter suddenly in performing a mitzva. For then, one's mind is not yet composed and is unable to think on what he is doing. Rather, one should ready himself to the matter and slowly prepare his heart for reflection.

The former two entice the mind and draw it towards ulterior motives, like an adulterous wife who, while still married to her husband, takes other men. Ulterior thoughts are referred to as "lewdness of the heart", as written: "and you shall not stray after your hearts and after your eyes which you go after promiscuously (Zonim)" (Bamidbar 15:39). For the heart strays from the whole aspiration which it should have bonded to, and turns instead to the worthless and imaginary falsehood.