Regarding things that come from the heart, enter the heart. Hence, why do we see that even if things have already entered the heart, one still falls from his degree?
The thing is that when one hears the words of Torah from his teacher, he immediately agrees with his teacher, and resolves to observe the words of his teacher with his heart and soul. But afterwards, when he comes out to the world, he sees, covets, and is infected by the multitude of desires roaming the world, and he and his mind, his heart, and his will are annulled before the majority.
As long as he has no power to judge the world to a scale of merit, they subdue him. He mingles with their desires and he is led like sheep to the slaughter. He has no choice; he is compelled to think, want, crave, and demand everything that the majority demands. He then chooses their alien thoughts and their loathsome lusts and desires, which are alien to the spirit of the Torah. In that state he has no strength to subdue the majority.
Instead, there is only one counsel then, to cling to his teacher and to the books. This is called “From the mouth of books and from the mouth of authors.” Only by cleaving to them can he change his mind and will for the better. However, witty arguments will not help him change his mind, but only the remedy of Dvekut (adhesion), for this is a wondrous cure, as the Dvekut reforms him.
Only while one is inside Kedusha (Sanctity) can one argue with oneself and indulge in clever polemics, that the mind necessitates that he should always walk on the path of the Creator. However, one should know that even when he is wise and certain that he can already use this wit to defeat the Sitra Achra (other side), one must bear in mind that all this is worthless.
This is not an armament that can defeat the war on desire, for all these concepts are but a consequence he has attained after the aforementioned Dvekut. In other words, all the concepts upon which he builds his building, saying one must always follow in the path of the Creator, is founded in the Dvekut with his teacher. Thus, if he loses the foundation, then all the concepts are powerless, since they will now be lacking the foundation.
Hence, one must not rely on one’s own mind, but cleave once more to books and authors, for only that can help him, and no wit and intellect, as they are lifeless.