The Lord freed us from Egypt by a mighty hand, by an outstretched arm and awesome power, and by signs and portents. It is necessary to explain the contradiction found in two biblical verses. In one we read, "I will pass through the land of Egypt on that night and I will smite the first born in the land of Egypt, both man and beast…I am the Lord." (Exodus 12:12) This implies that God Himself smote the first born, as the author of the Haggadah writes, "I and not another." In the other verse, we read, "None of you shall go outside the door of his house until morning...and not let the destroyer enter and smite your home." (Ex. 12:22) This verse implies that the death of the first born was carried out by a messenger and not by God. That is why the Israelites could not go out on the night of the tenth plague. Once the destroyer has been given permission to destroy (instead of God doing it), it did not distinguish between innocent and guilty. I heard the following explanation for this contradiction from my grandfather, Rabbi David Tevele Sheier, of blessed memory. The Egyptian houses were struck by a messenger of God. When they witnessed the death of the first born, they fled from their homes to Israelite households which had blood on the door posts. They Egyptians understood that God's messenger was not given permission to enter an Israelite house. It was only then that the Holy One Himself entered the Israelite homes and struck down the remaining Egyptian first born while the Israelites were protected. "I and not another" applies specifically to the Israelite homes in which the Egyptians took refuge, and the verses no longer contradict one another. The words of my grandfather speak from the grave.