My (LDS) mission was a unique experience for me because we were expected to devote all our time and attention to it. That was extremely difficult and often unpleasant, especially at the beginning, but it was achievable. By the end of my mission, I reached a point where I was able to do it without reservation.
College and jobs rarely are worth all your time and attention like my mission was. In recognition of this, our culture has the standard 8-hour workday expectation. A block of time is scheduled for working so that your employer hopefully gets a certain amount of work out of you, and the rest of the time is free so you can do more worthwhile things. (Unfortunately, college is less structured in that way. It tends to suck up far too much of students' time).
Do you think Einstein stopped thinking about physics after 5 pm? I doubt it. His work was worth all his time and attention.
This is my life goal with regard to my career: I want whatever I'm doing to be worth throwing my whole soul into (I'll call this a "soul-worthy pursuit"). I want to be as devoted to my work as I was to my mission. This is what "living the dream" means for me. I don't want to be at a job until 5 and then come home to work on the side projects that I actually care about. I haven't achieved this yet, but I've been longing for it.
What makes something worth all your time and attention? The book "Primed to Perform" talks about three "direct motivators:" play, purpose and potential. Play roughly means that you enjoy doing the task (though that's too simple of an explanation to do it justice); this is achieved by taking advantage of your unique talents and interests. Purpose means the task is beneficial to others. Potential means that the task is preparing you to achieve greater play and purpose in later experiences. The soul-worthy pursuit is the one that maximizes these direct motivators.
In "Man's Search for Meaning," Victor Frankl discusses three sources of meaning: 1) by doing a work or accomplishing a feat, 2) by loving someone, 3) by suffering. Considering only the first source, this soul-worthy pursuit is the meaning of your life.
There are two challenges: first, you must discover your soul-worthy pursuit. Second, you must pursue it. What is my soul-worthy pursuit? First I'll list some observations, and then I'll state my current answer to that question.
I love programming. I love thinking creatively and logically. I love thinking about radical ways to make systems better. I love music and the deep emotions it brings to me. I've noticed problems in life that I want to fix. Music recommendation systems aren't as good as they could be. I want to create a startup to fix that. As I've worked towards that goal, I've seen problems that are much deeper. Preparing for the startup by going to college and getting a temporary full-time job have caused me to have as main responsibilities things that aren't worth all my time and attention. This comes from a combination of inefficiency (especially in college) and focusing on problems that I don't really care about (especially at work).
That being said, I'm done with college already and I'll be done with my job soon enough too. But I still care about these problems. I don't want other people (for example, my future kids) to spend so much time and energy on things that aren't worth it for them.
I believe the meaning of my life is to help others find and fulfill their soul-worthy pursuit.
The inefficiency problem can be solved just by building a better system, about which I've already written with regard to education. But the need to work on problems you don't care about seems much more deeply rooted. It comes from the fundamental problem that there's more supply for things that are enjoyable to do. The high-paying tasks are often the ones that people don't want to do. How can this be solved?
The key is in our individual differences, specifically our talents and interests. If everyone was the same, the problem would be unsolvable. Some people would have to do the jobs that nobody likes, and those people would get paid more. But inasmuch as people have differences, we can take advantage of those differences to increase the amount of play people can experience. In this imperfect world, this will only be possible to a degree. There will always be things that need to be done that no one wants to do. But the key is to maximize the amount of energy people spend on soul-worthy pursuits. This is the meaning of my life.
 I do mean this within reasonable bounds; people need time to spend on other needs like relationships, sleep, food, fun, etc.
 This is a variation of Victor Frankl's, which he said was to help others find the meaning of their life.