Matthew Poole and continuators on Exodus 6:12

12 And Moses spake before the LORD, saying, Behold the children of Israel have not hearkened unto me, how then shall Pharaoh hear me, who am of uncircumcised lips :

(i. e.) Of polluted lips. Uncircumcision, being a great defect and blemish, whereby men were rendred profane, contemptible, and unfit for many services and priviledges, may note any defect, whether moral and of the spirit, or natural and of the body. So here it notes Moses his inability to cloath Gods commands in such words as might prevail with Pharaoh. But this was a great weakness of faith, as if God could not effect his purpose, because the instrument was unfit.

Marginal references: chap. 4. 10.