'Unclean' in the Bible

And Moses, answering the Lord, said, See, the children of Israel will not give ear to me; how then will Pharaoh give ear to me, whose lips are unclean?

And Moses said to the Lord, My lips are unclean; how is it possible that Pharaoh will give me a hearing?

And if you make me an altar of stone do not make it of cut stones: for the touch of an instrument will make it unclean.

You shall redeem the firstborn of a donkey with a lamb; but if you do not redeem it, then you shall break its neck. You shall redeem all the firstborn of your sons. None of you are to appear before Me empty-handed.