Joy is a “reflection” of good deeds. If the deeds are of Kedusha (Sanctity), hence joy appears. However, we must know that there is also a discernment of a Klipa (Shell). In order to know if it is Kedusha, the scrutiny is in the reason. In Kedusha, there is reason, and in the Sitra Achra (other side) there is no reason, since another god is sterile and does not bear fruit. Hence, when one comes by gladness, one should delve in words of Torah in order to discover the mind of the Torah.
We must also know that gladness is discerned as sublime luminescence that appears by MAN, [1] which is good deeds. The Creator sentences one where one is. In other words, if one takes upon himself the burden of the Kingdom of Heaven for eternity, there is an immediate sublime luminescence on that, which is considered eternity, too.
Even if one evidently sees that one will soon fall from one’s degree, He still sentences one where one is. It means that if one has now made up one’s mind to take upon himself the burden of the Kingdom of Heaven for eternity, it is considered wholeness.
However, if one takes upon himself the burden of the Kingdom of Heaven and does not want that state to remain in him forever, this thing and this deed is not considered wholeness, and naturally, the Upper Light cannot come and rest on it. This is because it is whole and eternal, and it is not about to change. With a person, however, even if he wants, the state one is in will not be eternal.