Whenever God said something of high importance to the people both in the old and the new testaments, or if it was something that had to be passed on to the next generations to read, God would always command His soldier to write down His words.
Below are just a couple of verses when once God Himself wrote and gave the tablets to Moses and another verse where God specifically commands John in the book of revelation to write His words down,
The tablets were the work of God, and the writing was the writing of God, engraved on the tablets. Exodus 32:16
Write this down, for these words are trustworthy and true. Revelation 21:5