Sakuyu-sama
This is Kawaguchi Hidetoshi. This is my humble answer to the question.
As Mr. Urakami said, there was no printing technology in the past, so copying the characters of the sutras on paper with a brush was used for studying and reciting sutras, and as sutras spread through this “shakyo,” Buddhist teachings also spread to various regions. In particular, many sutras were copied by the monks who went to mainland China to study Buddhism as envoys to the Sui and Tang Dynasties, so Buddhism was brought to Japan.
As an authority on the merits of transcribing sutras, there is “... acceptance, reading, interpretation, explanation, and writing of the Myōhō Ke Sutra...” in Hokke Sutra and Hoshibin 10, I believe that from where merits in writing are explained, eventually, the meaning of profit (riyaku), memorial service, or prayer was also included.
However, I believe that in order not only to “copy the sutras” mechanically and operationally, but in order to turn it into a true merit, profit, and memorial service, it is still most important to have a firm understanding of the content and put that teaching into practice.
In the sutras, the “Heart Sutra” is the most familiar and famous, but how many people actually understand what its content is, and can it be said that it has been put into practice based on that teaching... I think there are places that are extremely strict even though it is unauthorised.
Of course, it is actually difficult to fully understand the idea of “sky” described in the Heart Sutra, but it is extremely important in defeating ignorance (fundamental ignorance) and distress, which is the cause of our hesitation and suffering.
By all means, I would be happy if you could not only “copy the sutras,” but also thoroughly study and examine what kind of content it actually has, actually make use of that teaching as your own, and connect it to merit (accumulation of good deeds).
Kawaguchi Hidetoshi Gassho