HOCHMA: KIDDUSH LEVANAH קִדּוּשׁ לְבָנָה

KIDDUSH LEVANAH קִדּוּשׁ לְבָנָה :

– PRAYER OF CONCESSION ON FIRST FULL MOON

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.

-Baal HaSulam, Shamati, page 80-81