Commitment is caring deeply about something or someone. It is deciding carefully what you want to do, then giving it 100%, holding nothing back. You give your all to a friendship, a task, or something you believe in. You finish what you start. You keep your promises.
Being purposeful is having a clear focus. Begin with a vision for what you want to accomplish, and concentrate on your goals. Do one thing at a time, without scattering your energies. Some people let things happen. When you are purposeful, you make things happen.