Music lessons generally involve learning the technique to play a specific instrument or learning the rules, patterns, and jargon of a particular music culture. However, those nuts and bolts do not address questions of why we bother with this music stuff in the first place.
I've heard explanations like, 'music is part of what makes us civilized', or 'music is food for the soul', or simply, 'music is wonderful and enriching'. Clearly, those answers don't really tell us anything. In some cases, we tend to hear about extramusical side-effects, such as learning teamwork or that music involves mathematics. Certainly, music is one of the many forms of play that develop all sorts of general skills, but as many of us sense, music can be deeper than just playing around.
Perhaps the main drive to music is simply that, for most people, it achieves a strong emotional response. How that happens is certainly worth studying, and that is a substantial aspect of the field of music psychology. Music can have useful functions as well. We use it to control our sense of time, coordinate groups of people, support rhythmic physical activity such as repetitive labor or exercise, augment verbal expression, control moods, entertain, assist in memorizing, and more.
There is an unlimited number of different pieces to learn and techniques and styles to study. Without an understanding of what music is and why we use it, music study can lose direction and meaning. With such understanding, we can prioritize and focus on the specific skills, techniques, and pieces that achieve our practical goals. We can more effectively teach, write, practice, and appreciate music. I strongly believe that no technique or theory should be taught without also explaining its purpose (or at least asking the questions if the answers aren't yet known).