When the Black Plague killed about 25 million people in Europe in the 1300s, no one knew what caused it. The people were mostly devoid of any type of hygiene or sanitation such as washing hands, washing clothes or even bathing. The idea began to emerge that it was the Jews fault because they were dying at a lesser rate than other people. The people began persecuting the Jews for this reason.
The plague was actually caused by fleas biting infected rats and then biting people. However, the reason the Jews were more protected from the plague was that they followed the Scriptural Laws of Cleansing. The Book of Leviticus mentions washing with water 24 times. The Jews that followed the Biblical Laws of Cleansing protected themselves from an unknown danger. We may not know that there is danger in our path, but following God’s Laws protects us even though we are not aware there is danger.