The phrase implies that you should give something your undivided focus and resources, not just a part-time effort. He decided to devote himself to his startup, working long hours every day.
Pro Tip 2/3
Personal Choice
Usually, it indicates a personal decision to concentrate on something important to you, based on your values or passions. She devoted herself to charity work, finding great personal fulfillment in helping others.
Pro Tip 3/3
Time Intensive
It suggests that what you are committing to will take a significant amount of your time, possibly at the expense of other activities. He made the choice to devote himself to mastering the guitar, even if it meant less time for socializing.