Exodus 13:14-15

14  a And when in time to come your son asks you, ‘What does this mean?’ you shall say to him, b ‘By a strong hand the  Lord brought us out of Egypt, from the house of c slavery. 15 For when Pharaoh stubbornly refused to let us go, the d  Lord killed all the firstborn in the land of Egypt, both the firstborn of man and the firstborn of animals. Therefore I sacrifice to the  Lord all the males that first open the womb, but e all the firstborn of my sons I redeem.’
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