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Passover is a Jewish holy day established by God through Moses in the OldáTestament to commerate the liberation of Israel from bondage in Egypt. The name comes from the "Passing Over" by the angel of death, of the Israelite homes which had the blood of the Passover Lamb smeared on their doorposts during the last of the 10 plagues when all the firstborn of Egypt were slain.
Please read Exodus chapter 12.
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