Taken from Tanya chapter 40
Why love and fear are only considered wings-Love without Avoda is lacking its purpose:
Love and fear of G-d are in truth enumerated among the 613 commands, [and thus deserve to be considered Mitzvos in their own right and not to be given the secondary status of mere wings which are not an intrinsic part of the bird, and do not invalidate it]. Nonetheless, they are only described as wings being that the main purpose of the [Mitzvah to] love Hashem, is to serve Hashem [and fulfill the remaining 612 Mitzvos] with this love. [Thus, the Mitzvah to love Hashem is given a secondary-wing-status in comparison to the other Mitzvos, which its main purpose is to fulfill with that love.] Love without service of G-d is only relevant to the higher form of love called Ahavah Betanugim, as explained next. However, anyone who has not reached this state of love called Ahavah Betanugim, to have a taste of the World to Come, and rather his soul still thirsts for G-d, then he must quench his thirst in the waters of the Torah, which is the service of G-d that the love brings along. One who does not do so, and leaves the thirsting love in place without quenching it, is similar to a person who is standing by a river of fresh water and is screaming “I need water, I need water.” On this the prophet complains, “Ho, whoever is thirsty go to the water.” The intent of this statement of the prophet is not just the obvious, that one who thirsts to learn Torah should go learn Torah, but rather that one who thirsts for G-d, should go learn Torah and serve Him, as that will quench his thirst.
The Divine lesson:
Many people mistakenly believe that the main fulfillment of religious observance is accomplished through loving G-d in one’s heart and having a relationship with Him, while the actions of the Mitzvos are not as important. Here the Alter Rebbe calls out this philosophy as misguided. Hashem, who one is professing to love, desires that one fulfill his commands, the Mitzvos, and that is the entire purpose of the love. It is only the Mitzvos that accomplish the true Dveikus to Hashem, and thus, if in truth one really loves G-d, it must bring to fulfillment of Mitzvos, as only that brings about the closeness that one is professing to desire to have for Him. One who says the main duty is of the heart, and does not fulfill the Mitzvos properly, is like one who professes his love for his wife in his mind, but fails to perform actions that express that love. The wife will not feel loved simply by hearing of his passion for her and needs to see actions of love performed. A further point, everyone has a love language, which the lover must tune into if he truly desires to express that love to the person. A husband must learn his wife’s love language that talks to her heart if he truly desires to love her on her terms. So too, Hashem, His love language is the Mitzvos, and only by fulfilling them does one express love on His terms.
Ahavah Betaanugim-A love which is a service in its own right:
Love of which its purpose is not to motivate service of G-d, but rather is a purpose in it of itself, only applies to the higher form of love called Ahavah Betanugim, a love of delights. This love entails receiving pleasure in one’s Dveikus to Hashem, similar to the reward in the World to Come. This love is not common today being that it is given as reward for the service, and the service is meant to be done now, prior to the reward.
 As explained in Bava Kama 17a