Hi. You did not enter the text to which this question refers, which makes it impossible for it to be answered. However, I will try to help you as best I can.
The author explained a scientific concept because he wanted readers to understand the meaning of that scientific concept, which would allow the reading of the text to be more convenient and efficient for the reader. The decision to explain the scientific concept through a historical event was to show how this concept fits into the real world. The use of the reference, on the other hand, was intended to extend the explanation by showing another application of the scientific concept, making it even more understandable.