The problem is that the prophets tell you that scribes changed what God had written from the beginning, and so God became man and came to show us the true Law of God.
And Moses received the Law, but later scribes changed the law of God, as say the prophets. The prophets tell us so:
"...but my people know not the ordinance of the LORD. "How can you say, 'We are wise, and the law of the LORD is with us'? But, behold, the false pen of the scribes has made it into a lie". (Jeremiah 8:7-8)
"Woe to those who give wicked laws and scribes who write tyrannical prescriptions to set aside the poor and violate the rights of the underdog of my people, to rob widows and orphans" (Isaiah 10.1 -2)
"And the land is defiled under its inhabitants, because they have transgressed the laws, changed the commandments, broken the everlasting covenant" (Isaiah 24: 5-6).
"He says, therefore, the Lord: Because this people draw near me with their mouth, and honor me with their lips, but their heart is far from Me, and their fear of me is a commandment of men which have been taught" (Isaiah 29.13).
And Jesus Christ, remembering the words of the prophet Isaiah, also told the scribes and Pharisees who were teaching the commandments of men:
"Hypocrites, well did Isaiah prophesy of you, saying,
This people honors me with their lips;
But their heart is far from me.
But in vain they do worship me,
Teaching for doctrines commandments of men" (Matthew 15.7-9
Dear friends, this is what happened, what the prophets tell us: The God's law was changed by the scribes. For this reason, the Old Testament's law is different to the commandments of Jesus Christ.