| Nedarim
The mitzvah of Talmud Torah has a dual objective. First and foremost, one learns so one will know how to act: "an ignoramus cannot be a righteous person" (Avot 2:5). However, learning is so much more than a utilitarian function enabling us to perform mitzvoth. One can often learn how to do mitzvoth by observation without any formal education. Talmud Torah is primarily how we connect to the word of G-d, helping us to gain an understanding of the Divine and hence, of the human condition.
That the primary focus of Torah learning is to be involved in Torah can be seen through a Talmudic discussion regarding vows. Ein shevua chal al shevua, a vow cannot take effect on a pre-existing vow. A vow to abstain from eating for a day is a meaningless one if one has already taken a vow to fast for, say, three days. One's vow to perform mitzvoth--to keep kosher or to refrain from chametz on Pesach--is likewise a meaningless vow, as the one taking such is already foresworn from Sinai regarding such. Torah is not something we may choose to observe or ignore. Its obligations are incumbent upon us from birth as a result of the oath taken by our ancestors some 3,300 years ago at Sinai.
Yet this principle seems to fly in the face of the teaching of Rav Gidal in the name of Rav who, quoting the biblical verse "I have sworn, and have confirmed it, to observe Thy righteous ordinances" (Tehillim 119:106), teaches that one may "take an oath to perform mitzvoth"(Nedarim 8a). To resolve this contradiction, the Gemara notes "to encourage oneself it is allowed." There is little doubt we feel more bound by a vow we take ourselves than one taken by our ancestors thousands of years ago[1]. Such a vow, while unnecessary in theory, in practice gives us the motivation to do that which we should be doing--but find difficult to do. As we all know, motivation is most difficult, whether it be for mitzvoth, exercising, going on a diet, or quitting smoking. If it takes a vow to motivate us, so be it. It is for this reason a pledge to give charity is so useful.
Once we have established that one may take a vow to motivate oneself to perform mitzvoth, the Gemara is perplexed by a second teaching of Rav Gidal in the name of Rav that "one who says I will arise and learn this chapter, learn this masechet, he has taken a great vow to the G-d of Israel". Here, too, he is sworn from Sinai to study Torah, so such a vow seems superfluous. And to argue that such a vow is meant to motivate one to learn Torah--such may be true, but Rav has already taught that vows to motivate mitzvah performance are allowed, and perhaps even praiseworthy.
While it is true that one is obligated to learn Torah, how much and what one must learn is not covered in the oath taken at Sinai. In theory. one could fulfil the mitzvah of Talmud Torah--our Sinatic obligation--by reciting Shema morning and evening. Learning an entire masechet is a wonderful additional obligation one takes upon him- or herself.
Furthermore, even if one were to accept that one must learn much more than reciting Shema, there is no specific obligation to learn a particular piece of Torah. A Jew is obligated to learn; what we learn is much less important. It is the process that is most important. We must seek out the word of G-d--and there are so many forms to choose from. We, thankfully, have no obligation to learn the entire Torah, but we do have an obligation whenever we can to engage with Torah.
[1] The Gemara notes that in actual fact, G-d had to place a mountain over our heads to ensure that we would accept the Torah. As Torah was forced upon us, we cannot be held liable for violating its precepts. Only when the Jewish people voluntarily reaccepted the Torah at Purim time did our vow of acceptance become fully operational (Shabbat 88a).