Rabbi Meir would say: Whomever studies Torah for Torah's sake alone merits many things…
The sages say, “He who performs (good deeds) not for the sake of the good deed itself, it would have been better for him had he not been created.” On the other hand, the sages also say, “One should always engage in Torah study and mitzvah performance, even if it is not for its own sake because acting with ulterior motive will eventually become acting for its own sake.” Rashi and Tosafot explain that “it would have been better for him had he not been created” refers to a person who studies Torah only in order to denigrate it, or someone who does not practice what he learns. Other categories of Torah study are found in people who study Torah in order to garner respect, those who study Torah out of fear of Divine retribution, or those who study Torah in order to receive reward in this world or the next. All these categories of Torah study are relatively low levels, and it is preferable not to engage in them.
The relatively higher level (higher than the ones just mentioned) of learning Torah “not for its own sake” is attained when a person studies Torah in order to rectify his soul and to connect it to God by means of the Torah—to quench his thirst for God through Torah, which is likened to water, “water is none other than Torah.” It is about this level that the sages prescribed, “One should learn Torah [even if it is] not for its own sake.” This is because there is a principle that initially, a person does things because his soul desires them. This level of Torah study can be likened to the relationship between a bride and groom. The bride is the individual learning Torah, and the groom is the Torah, which showers its abundance on him, just as the groom does for his bride. There is yet a higher level, similar to this one, where the individual learns Torah not for the sake of his personal soul’s rectification, but for the rectification of the all-inclusive soul of the Jewish people—the root of all the souls of Israel. Of course, his individual soul will receive light, as well.
Still, even these higher levels are still relatively Torah study not for its own sake. True “Torah study for its own sake” is when a person studies Torah for the sake of the Torah, itself—in order to bind the Torah with its source in God’s infinite light. An example of a person who engaged in this lofty form of Torah study is King David, who would bind the Torah above with the Holy, Blessed One.
When a person learns Torah for this purpose, he is described as a groom or an influencer and the Torah is described as his bride or recipient. This level is possible only after he has achieved the previous level: First, a person studies Torah in order to rectify his own soul and cleave to God (with the Torah above him). By doing so, he merits the revelation of the supernal source of the souls of Israel, which is above the Torah: “The thought of (creating) Israel preceded everything.” Only then does he becomes one who benefits the Torah.
The higher level of “not for its own sake,” for the rectification of the learner’s own soul, is relevant to the service of the intermediate person, the beinoni in the Tanya. The level of “for its own sake,” for the sake of the Torah alone, is relevant to the service of the tzaddik. The intermediate individual cannot achieve consummate service of God exclusively for the sake of the unification of God and His Shechinah. He will always have some sort of personal interest. Only the consummate tzaddik, who completely identifies with his Divine soul and can serve God exclusively for the sake of Heaven, like a son who loves his parents more than he loves himself, can reach this level.
 Berachot 17a.
 Pesachim 50b.
 Rashi and Tosafot to Berachot 17a.
 Tosafot to Pesachim 50b, Tosafot to Sotah 22b. More in Rabbi Schneur Zalman of Liadi’s Hilchot Talmud Torah 4:3.
. Baba Kama 82a.
 Pesachim 68b.
 Sefer Habahir 196.
 Breishit Rabbah 1:4.
 Until here are the words of the Alter Rebbe in Drushei Chatunah (siddur with Da”ch 128a). This is explained at length in Rabbi Ginsburgh’s book, “Chatan im Hakalah.”