They were just ordinary tablets of stone, until God wrote on them. They were probably rough, unhewn and useless. Because God touched them and wrote on them, they became special and precious. God used them to write what we now call The Ten Commandments and from these were based His command to us which amalgamated all ten.
‘Love God with all your heart, with all your understanding and with all your strength and love your neighbour as yourself’ Matthew 12:33
Before we have the touch of God we are rough, unhewn and useless. Once God has lovingly touched us, we are useful and precious.