Just a point of clarification. God wrote the 10 commandments but these were destroyed by Moses. Moses wrote the second set of the 10 commandments under God's command. Do you believe what Moses wrote was any different that what God wrote? Now if Anselm said there was an 11 commandment and the Church agree, would you agree that Anselm's 11 commandment was at the same level as what Moses' wrote?
Exodus 34:
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Then the LORD said to Moses, “Write down these words, for in accordance with them I have made a covenant with you and with Israel.”
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So Moses stayed there with the LORD for forty days and forty nights, without eating any food or drinking any water, and he wrote on the tablets the words of the covenant, the ten commandments.
We have no Scriptural or other evidence that the NT was written in this fashion. I believe that Moses wrote as was dictated based upon these verses.
The hypothetical Anselmic 11th commandment? I put my trust in the Church of Jesus Christ to keep the doctrine pure; I don’t believe that there would be that 11th commandment.