John Gill Commentary Deuteronomy 4:2

"Ye shall not add unto the word which I command you, neither shall ye diminish from it, that ye may keep the commandments of Jehovah your God which I command you." — Deuteronomy 4:2 (ASV)

You shall not add to the word which I command you, neither shall
you diminish anything from it
Neither make new laws of their own, and join them to the law of God, and set them upon a level with it, or prefer them before it; as the Scribes and Pharisees did in Christ's time, who by their traditions made the word of God of none effect, as do the Papists also by their unwritten traditions; nor abrogate nor detract from the law of God, nor make void any part of it:

Or else the sense is, neither do that which is forbidden, nor neglect that which is commanded; neither be guilty of sins of omission nor commission, nor in any way break the law of God, and teach men so to do by word or by example; not a jot or tittle is either to be put to it, or taken from it, (Proverbs 30:5Proverbs 30:6) (Matthew 5:18Matthew 5:19) (Revelation 22:18Revelation 22:19)

that you may keep the commandments of the Lord your God, which I command
you ;
in his name; or which he delivered unto them as his commandments, and which were to be kept just as they were delivered, without adding to them, or taking from them.