Deuteronomy 4:2 Do not add to what I command you and do not subtract from it, but keep the commands of the Lord your God that I give you.
When Moses had to give the people explanations from God as to what to do, He was given very strict instructions which had to be explained in full – and remembered.
Nowadays we have this all written down in our Bibles so we can refer back to things all the time with ease... and we also have a new way of life!
Back then the instructions were strict because the people had to change their ways and learn to live for God.
We now have this all as examples for us to live by – don't ignore it!