John Wesley on Exodus 31:18

These tables of stone, were not prepared by Moses, but probably by the ministry of angels. They were written with the finger of God - That is, by his will and power immediately, without the use of any instrument. They were written in two tables, being designed to direct us in our duty, towards God, and towards man. And they were called tables of testimony, because this written law testified the will of God concerning them, and would be a testimony against them if they were disobedient.