God Commanded "Do not add or take away from MY word".
The perfect one who gave the Torah gave it perfectly. If we add something or take something away from it, what we are saying is, it isn't perfect, we are going to make it better. When we add something to it or take away from it, it is no longer the Lord's perfect word. It is man's word.
Isaiah 2:3
People from many nations will come and say, “Come, let us go up to the mountain of the LORD, to the house of Jacob’s God. There he will teach us his ways, and we will walk in his paths.” For the LORD’s teaching will go out from Zion; his word will go out from Jerusalem.
(this is when Yeshua returns for the 1,000 year millennium)