I don't recall anything in Revelation at the moment, but see these words from Isaiah:
"Then said I, Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the LORD of hosts.
Then flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar:
And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged." Isaiah 6:5-7
God knows our frailties. In Isaiah we see that he needed some work done on his mouth before he could speak to other people about their troubles. When we look back to Moses, we see that he tried to convince that he could not handle the job God has chosen him to do. God doesn't want someone who is too strong in himself. If He does choose such a person, He has to humble him before he is ready to get it done. All of us need to be humbled so God can then remold us into something useful in His plan.
See Moses in the beginning of his calling:
"And Moses said unto the LORD, O my Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue.
And the LORD said unto him, Who hath made man's mouth? or who maketh the dumb, or deaf, or the seeing, or the blind? have not I the LORD?
Now therefore go, and I will be with thy mouth, and teach thee what thou shalt say.
And he said, O my Lord, send, I pray thee, by the hand of him whom thou wilt send.Exodus 4:10-13
But then see Moses later when his own brother and sister came up against him:
Num 12:3 (Now the man Moses was very meek, above all the men which were upon the face of the earth.)
Moses had changed, had been changed.
I remember early in our walk with God, my wife used to call be Moses because I was so hesitant to open my mouth. That was a great many years ago. Moses I'm not, but God has at times used me when I have surrendered to his will. Somewhere along the line a seraphim may have touched my mouth with a live coal.