We'll the Isrealites enslaved in Egypt said that their Lord is a Jealous God and all those who do not worship him will be damned to a lake of fire.
But I have hardened my heart.
I have hardened my heart just like the Pharaoh of Egypt hardened his when he would not let the'yer people go.
And so Moses saw to it that first born man was slain in the name of YHVH.
And in blood those that believed in their Lord were spared.