Why it is important to understand intervals to an organist?

From time to time, I post some articles and videos about some elements of music theory, such as scales, intervals and chords. Sometimes, people want to know why the theory of interval construction and their resolution should be of interest to an organist? Isn't the goal of many organists to learn and play the most beautiful organ music ever composed? In other words, what does the theory have to do with practice? Here is my answer to this question in this video.