The Rebbe's guidance on Torah study and earning a living:
For bochurim: learn now, and don't let worry about the future disturb the learning. Young students should stay devoted to Torah study rather than worry about future livelihood; trust in Hashem, and diligent learning now is the strongest foundation for a livelihood later (IK 2025, 3952, 5017, 6184, 6587). Enthusiasm for full-time learning should be supported, not dampened (IK 10507). Spending time devoted to learning before making career decisions brings clarity and peace of mind (IK 7436).
For parents: don't take a son out of yeshiva for a trade for financial reasons. Financial concerns should not override a child's Torah study, and children's learning itself brings blessing to the family, including in livelihood and health (IK 3614, 4883).
For those who work: Torah stays central. Earning a living is necessary for many, but set fixed times for Torah study, and wherever possible keep learning at the center (IK 1641, 4656). Fixed times for Torah are themselves a channel for blessing, materially as well as spiritually (IK 3163, 4452, 6135). Balance the job with spiritual growth and family (IK 6164).
See also: פרנסה – ביטחון ודאגה; שידוכים – עיכוב הנישואין.