Cross reference
Exodus 6:30
30 And Moses said before Jehovah, Behold, I am of uncircumcised lips, and how shall Pharaoh hearken unto me?
Exodus 6:12
12 And Moses spake before Jehovah, saying, Behold, the children of Israel have not hearkened unto me; how then shall Pharaoh hear me, who am of uncircumcised lips?
Exodus 4:10
10 And Moses said unto Jehovah, Oh, Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant; for I am slow of speech, and of a slow tongue.
1 Corinthians 9:16-17
16 For if I preach the gospel, I have nothing to glory of; for necessity is laid upon me; for woe is unto me, if I preach not the gospel.
17 For if I do this of mine own will, I have a reward: but if not of mine own will, I have a stewardship intrusted to me.