They were doing it (memorize the Koran) only to learn how to sing the chants. Just like jewish was also singing Torah as a chants but they were never studying what inside the text contained in their singing.
I have a notice a few moslem here they were never understand the arabian text that they sing in chants. This man made rituals was made God mad in Isaiah 29:9-16, because they only do this ritual as told but they never seek God in the spiritual realm and 10 commandments of Moses was not in their main concern.
In catholic singing chants only for Psalms as David had wrote the psalms and sing this chants to God (Psalms 3 - Psalms 9).
Chants in jewish :
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Who Made Up the Way We Sing the Torah?