Most of us believe in the idea of having a purpose to life.
Viktor Frankl - a well known psychiatrist, author and survivor of the Holocaust described in his book - Man's Search for Meaning, how this idea of purpose beats the very purpose of survival sometimes. During his time in the Nazi concentration camp, the idea of even surviving another day was a tough thought, leave aside any thought of his purpose while he went through yet another day of suffering and being lost.
In his popular school of thought - Logotherapy, he suggested to believe in things like a horse or a bull pulling a cart would. The horse/bull wouldn't know what cart they're pulling and what purpose it serves to even pull a cart. They don't know the impact they create while doing what they do, in the lives of humans. All they care about is the food and care they get at the end of their work. Even if you tell them what their purpose is, they would not understand since it is out of their comprehension abilities.
Similar to that, most of us go to our mundane looking jobs every day without knowing our purpose - in life and at work. A few years ago while I was still employed at a Big Four, I decided to break out of the rut and figure out what my job entails - and even though I was a very small part of a very big machinery, I understood the importance of my work and how it affects the system as a whole. My purpose back then was to ensure that the malfunctioning of a small nut-bolt in the machinery does not break the machine or slows it down. Four years later, I am a part of another machinery with a very varied purpose.
Our purpose in life is a variable.
It is not a constant thought. It follows the idea of Buddhism - one of the four noble truths - Impermanence. Be it at work, or in life in general - most of the times we go through life thinking and not understanding our purpose, but we do serve something at the end of the day. It may not be in our ability to truly and fully understand it; and it is ever changing.
As we go through in life, let's choose our own purpose, redefine old ones, and sometimes, let's not fret over the idea of our purpose and break our heads over the apparent lack of it or a clarity on it.