The explanation is as follows; there are two types of Simcha. This is due to Simcha generally emanating from the Avodah of love and there are two types of love. First, there is a logical love that when one contemplates how the true reward for a Mitzvah is the Mitzvah itself, one begins to appreciate the precious value and prominence of Torah and Mitzvos resulting in rejoicing in one’s Avodah.
This [level] is attainable by every single Jew; so that everyone needs to feel the precious value and prominence of Torah and Mitzvos and for this reason one’s Avodah should be with joy (Simcha). And when this Simcha is lacking in one’s Avodah, this is no mere absence of an element within the Avodah. On the contrary this shows that one is lacking in any kind of appreciation of the precious value and prominence of the Torah and Mitzvos.
However, all this above is regarding the type of love which makes sense according to logic. There is a [second] type of love however, which transcends logic being above reason and understanding, beyond any objective [at all], as the Tanya writes about the ‘B’nei Aliyah’ that their Avodah is not exclusively to cleave to Hashem alone. [This] to quench the thirst of their soul which longs for Hashem. But as the Tikunim explain in the words of the Zohar: אֵיזֶהוּ חָּׂסִּיד הַמִּתְּחַסֵד עִּם קוֹנוֹ “Who is a Chossid? One who does kindness with his Master”, and the Tikunim says: “Read the word קוֹנוֹ (which we translated as Master) to read עִּם קַן דִּילֵיהּ “with His nest”. To unite HaKodosh Boruch Hu with his Shechinah in the lower realm. [Thus, making HaShem a nesting place in this world.]
It is regarding this, that the Possuk states: שִּמְּחוּ צַדִּיקִּים בַה׳ “Rejoice you righteous with Hashem” because this is the Simcha that comes from a love which transcends logic, and not all Yidden are able to love in this manner. Only Tzaddikim have this ability. It is a gift from above.
