Ok, here it goes!
The Lord came down amongst men as the angel of the Lord and confused their language, just as how a beguiling spirit came to earth to confuse muhammad!
You must understand the angel of the Lord is the incarnation of God, and the words "let us" is referring to the angel of the Lord with God indwelled within Him, or the Holy Spirit within Him.
Example:
And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him: And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased. Matthew 3:16,17
Do you see how the Spirit of God came down upon the Son?
The Angel of the Lord dwelled in the midst of these people unrecognized!
Ask yourself, did God allow for the Spirit of the False Prophet to deceive muhammad? YES!
WHY?
Don't know, be back!