Our Gemara cites a verse in Bamidbar (18:7):

וְאַתָּ֣ה וּבָנֶ֣יךָ אִ֠תְּךָ תִּשְׁמְר֨וּ אֶת־כְּהֻנַּתְכֶ֜ם לְכָל־דְּבַ֧ר הַמִּזְבֵּ֛חַ וּלְמִבֵּ֥ית לַפָּרֹ֖כֶת וַעֲבַדְתֶּ֑ם עֲבֹדַ֣ת מַתָּנָ֗ה אֶתֵּן֙ אֶת־כְּהֻנַּתְכֶ֔ם וְהַזָּ֥ר הַקָּרֵ֖ב יוּמָֽת׃ (ס)

⁦while you and your sons shall be careful to perform your priestly duties in everything pertaining to the altar and to what is behind the curtain. I make your priesthood a service of gift; any outsider who encroaches shall be put to death.

Commentaries note the language עבודת מתנה which translates either as a service of providing sacrificial gifts, or in more if a Derash sense, the service itself is a gift from Hashem.

The Baal HaTanyah expresses what I believe is one of his key theses in the Tanya through this pasuk. (תניא חלק ראשון ספר בינונים יד, תניא חלק שני שער היחוד ואמונה חינוך קטן)

Here is how I understand what he is saying, and I hope I do it justice:

The majority of people are what he calls “benonim”, which  literally translates as “average”, but as you will see is not really average. By definition, if it constitutes the majority of people then it cannot be the numerical average. What he means to say is that they occupy a middle zone, a median if you will, between good and evil. How he defines this middle zone is significant.

In the typical person, there is a desire to do evil, that is a desire for physicality and other sensual lusting. While a person may also gravitate and wish to do good, and desire to be spiritual, it is not innately within him. This is the status of the Benoni. The Benoni can, and should, strive to mindfully recognize the ethereal value and benefit of turning toward love of G-d and spiritual matters instead of physical matters. In time, he could train himself and convince himself more and more of the deep value of those pursuits. However, ultimately most people will still exist in the zone where their body craves sensual desires and experiences. That by definition, makes them into a Benoni.

Now there is the real person who is gifted with a different level of relationship to this world. Deep within his soul he has become so spiritual, that he naturally is repulsed by sensuality and physicality, and is naturally drawn toward the spiritual. This is a rare level to achieve and comes from a combination of lifelong spiritual work and a gift from G-d. This is what is being referred to in the verse as the Service of Gifts. That is, that Hashem can give a person the gift of being fully disposed and desirous of the good and spiritual.

Why does any of this matter? I believe it is harder to accomplish or work on self-development without a theoretical model and goal. The Baal HaTanya is providing a framework to understand the self within the maelstrom of urges and longings, spiritual and physical. We can know that it is within our choice to reach toward the ethereal, and begin to develop a deeper appreciation that could lead to a natural inclination. The physical has its charms but it is not eternal and doesn’t have much to offer beyond immediate satisfaction. To sum it all up, when a person is focused only on the immediate, it is hard to imagine anything else. When a person is focused on a broader sense of good, meaning, and spiritual connection, it also is hard to imagine anything else. Choose wisely my friends.