The Sifrei Kabbalah explains that the purpose of our work is to create a physical vessel in which to accept Hashem’s gift of livelihood. This gift originates in the form of a spiritual bounty at a very high level in heaven. It then descends from world to world, until it finally reaches us, where it must be transformed and adapted into the physical dimensions of this world. This is accomplished through our hishtadlus. By using the physical matter of this world in our work, we transform and receive the Divine, spiritual gift of parnassah in a form we can use and appreciate.
In summary, the purpose of work is:  To fulfill the Torah’s “curse” to all mankind.  To test our integrity.  So that life shouldn’t be too easy.  To create a physical means by which we can receive a spiritual bounty. But, it is not the work itself that gives us our parnassah, that is Hashem’s gift to us.
When we internalize this truth, the pursuit of a livelihood becomes a far happier experience. The holy sefarim call the pursuit of income, “The bitter and depressing quest for parnassah.” Many people can testify to the accuracy of this description. For many people, the struggle for a livelihood is “bitter and depressing.” However, when one believes that Hashem is the primary source for his parnassah, this bitter pursuit becomes much easier, knowing it’s not “all in our hands.”
The Kitzur Likutei Maharan writes: “Those who do not believe … eat the bread of affliction and they are always filled with depression and sadness…. But those who believe with perfect and true faith that their parnassah and wealth comes from Hashem alone [albeit that it is His will that people do some form of work, or hishtadlus, as explained above] they are attached to holiness, to life, to happiness.”
When one believes that parnassah comes from Hashem: (1) He will deal honestly, confident that he doesn’t have to cheat to get what he needs, (2) He will be happy with his lot, because he knows that Hashem has destined for him the portion that is for his ultimate best, (3) He won’t worry about the future, because he knows that Hashem is always there and able to support him. (4) The believer will also realize that it isn’t always necessary to work heavy jobs and many hours to earn a living. Since Hashem is the real Provider, He can provide for us with more moderate toil as well.
When we discover and internalize this great secret of the world, that we work for free and we eat for free, then the “bitter and depressing quest for parnassah” suddenly becomes the sweet and pleasurable experience of doing Hashem’s will. He wants us to work for our parnassah and to do hishtadlus, but we must always remember that the results of our hishtadlus is always in Hashem’s loving hands.