Passover and Philistines

Exodus 13 prescribes the rules for the Passover feast.  The first-born of all humans and animals belongs to Yahweh (and I'm assuming this means to the priestly caste who represents him on Earth).  For seven days in the month of Aviv (Spring) no yeast, no leaven, is to be eaten and this is to be a yearly feast. 

The use of the term "redeem" or "sacrifice" regarding the first-borns sons is a little confusing.  Surely they are not meant to be sacrificed as an animal is sacrificed.  Was it meant that they were to be sacrificed as servants of the priestly caste?  Later on this was taken to mean that they were to be redeemed by being dedicated to the study of the Torah, I believe, although I think that among the ultra-Orthodox in Israel all the sons are sent to do nothing but study the Torah (and, conveniently, avoid military conscription).  The redeeming of the first-born is meant to be the pay-back for Yahweh killing the first-born of the Egyptians, and leading the Israelites out of Egypt.

The first mention of the Philistines as warriors is in Ex. 13:17: 

When Pharaoh let the people go, God did not lead them on the road through the Philistine country, though that was shorter. For God said, “If they face war, they might change their minds and return to Egypt.”

 Then in Ex.15:14

¹⁴ The nations will hear and tremble;
   anguish will grip the people of Philistia.

In Ex. 15:20-21, Moses's sister Miriam is called a prophet, and she leads the women in battle-song, "with timbrels and dancing".  It's a pretty nasty song about smiting one's enemies. The Israelites also complain a lot. :-)