Mystery mnemonic

My boss decided to while away a few moments yesterday - this was the result:
Being faithful, God freed captive believers hardening low-down Pharaoh.

What is it you ask??? Yes, that is indeed the question! It's designed to be a helpful mnemonic - but can you work out what it's supposed to help you remember?
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Need a clue?
Which crucial Bible event does it refer to?
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Need another clue?
There are ten words in the phrase. Can you think of ten cataclysmic things linked with this Bible event?
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Want the answer?
It's a way of remember the Ten Plagues in order:
Being Faithful, God Freed Captive Believers Hardening Low-Down Pharaoh.
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Blood, Frogs, Gnats, Flies, Cattle, Boils, Hail, Locusts, Darkness, Passover.

Aren't you glad you know that?!