Oftentimes, repeating something over and over again makes it get stuck in your head. Like a lesson you learn in school or a certain skill like using special equipment, doing it in repetition often leads to mastering it. Singing bible verses is pretty much the same. You say the words in song, and repeat that and you think on what it means and understand it.
Singing bible verses is most useful when teaching it to children. Below is a short video that shows as an example: