Knowing music theory will help you to read music.
It seeks to identify patterns and structures in composers' techniques, across
or within genres, styles, or historical periods. In a grand sense, music theory distills and analyzes the fundamental parameters or elements of
music–rhythm, harmony (harmonic function), melody, structure, form,
texture, etc.

i. Basic to advanced level Trinity and Royal School - Syllabus grade 1-8

ii. Learning music theory to communicate with other musicians

iii. A knowledge of music theory gives you a context for the music you are playing