As one grows in his Emunah and Bitachon he realizes that H'shem can provide for him through any means. As such he will choose a profession that is easy, suitable, and comfortable knowing H'shem is providing for him, not his employment. Continuing to turn his heart to trust in H'shem will eventually bring him to the realization that he can trust Him in all circumstances in life and look for ways to use what he has to serve GD and fulfill his commandments.
469
Nefesh Hachaim
The amount of time and effort one should spend learning musar and building yirat H'shem should be just enough to be able to protect the Torah he is learning. It is wrong to spend one's majority of the time building the fence and neglecting putting in the effort to what it is meant to protect.
Gate Four. Chapter 8 pg 145,146
Alshich on Avos
Torah learning combined with working breaks the pattern of sin. The amount of effort one needs to put in to accomplish both earning a livelihood and learning Torah causes the angel that was created by the original sin to be disturbed and confused allowing the person to break free of its hold.
Chapter 2 Mishna 4 pg 64