Originally, it was incumbent upon every male Jew to write a kosher (valid) Torah scroll for himself, using ink and parchment. He was to study from this scroll throughout his life. However, once it became permissible to write down the Oral Torah (see below), sacred Torah scrolls were no longer used for study. They were reserved for communal Torah reading, while books (first handwritten, then printed) were used for study. Therefore, nowadays people fulfill the mitzva of writing a Torah scroll by buying Torah books to guide them how to properly observe the mitzvot.
