Exodus 9:33,34

Moses went out of the city Not only for privacy in his communication with God, but to show that he durst venture abroad into the field, notwithstanding the hail and lightning, knowing that every hail- stone had its direction from God. And spread abroad his hands unto the Lord An outward expression of earnest desire, and humble expectation. He prevailed with God; but he could not prevail with Pharaoh: he sinned yet more, and hardened his heart The prayer of Moses opened and shut heaven, like Elijah's. And such is the power of God's two witnesses, Revelation 11:6. Yet neither Moses nor Elijah, nor those two witnesses, could subdue the hard hearts of men. Pharaoh was frighted into compliance by the judgment, but, when it was over, his convictions vanished.