This question, asked by Rabbi Shimon ben Yochai, is one that has been pondered by dedicated Jews for generations. While the mitzvah of studying the Torah is compared in greatness to all other mitzvot, one must stll earn a livelihood.
Rabbi Shimon’s question is derived from a conversation about a verse in Deuteronomy 11, in which God promises that if the Jewish people keep His commandments then God will send the right amount of rain in the proper seasons so that “you (the Jewish people) will gather in your grain” (Deuteronomy 11:14).
Rabbi Shimon proposed his own answer, suggesting “that when Israel performs the will of the Omnipresent, their work is performed by others.” It is, however, important to note Rabbi Ishmael’s understanding of the verse: “And you shall gather in your grain.” Rabbi Ishmael sees in this verse an implication that one is to combine the study of them [the words of Torah] with a worldly occupation (Brachot 35b). The ability to combine these two vocations is part of the blessings of following God’s words.
There are, of course, some for whom studying Torah is their profession. In fact, when the 12 tribes were complete, the Tribe of Issachar dedicated itself to studying Torah while the Tribe of Zebulon worked to support them. Today, there are many Jews who have been able to follow Issachar’s path thanks to those who fulfill the role of Zebulon. Many others, however, live by Rabbi Ishmael’s ideal and choose to dedicate time for Torah study while working in other fields.