Memorizing the Chumash - the Written Torah

HH this morning I noticed a child testing his friend as he recited by heart verses of the Torah with their cantilation, and I found it odd, because the written Torah is written whereas the Oral Torah was originally not to be written only memorized, and thus the tradition was always to encourage memorizing the Oral Torah.

By Divine Providence, a mere few hours later, I came across the letter of the Vilna Gaon where he instructs that the children should first study the Chumash until they know it almost verbatim!

Na NaCh NaChMa NaChMaN MAyUMaN