Kodály said it was important to practise two-part singing from the very beginning and he wrote these 77 exercises to supply a need for something shorter and easier than the others in the series 66 Two-part Exercises to 22 Two-Part Exercises.
He believed that sight reading should at all times offer fresh material ... remaining attractive music, not merely mechanical exercises.
Movable Do helps the understanding of modulation and the musical significance of each note of a melody.