Exodus 12:29 (KJV) - 29 And it came to pass, that at midnight the LORD smote all the firstborn in the land of Egypt, from the firstborn of Pharaoh that sat on his throne unto the firstborn of the captive that was in the dungeon; and all the firstborn of cattle.
Numbers 3:13 (KJV) - 13 Because all the firstborn are mine; for on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I am the LORD.
Numbers 8:17 (KJV) - 17 For all the firstborn of the children of Israel are mine, both man and beast: on the day that I smote every firstborn in the land of Egypt I sanctified them for myself.
Keil-Delitzsch (Comm. on the OT, v1 - Num. 3:11-13, p. 20)
When He slew the first-born of Egypt, He sanctified to Himself all the first-born of Israel, of man and beast, for His own possession.... By virtue of this sanctification,...the nation was required to dedicate to Him its first-born sons for service at the sanctuary, and sacrifice all the first-born of its cattle to Him. But now the Levites and their cattle were to be adopted in their place, and the first-born sons of Israel to be released in return (v40 sqq).
Aaron's line evidently was already adequately pure to be the priestly class.
What made the blood of the Egyptian's at least 'pure enough' to sanctify Israelites (ultimately the Levites) to tend the sanctuary?
What was wrong with the cattle of the Israelites that the first-born cattle of the Egyptians also had to be slain? They didn't even do animal sacrifice in the wilderness for 40 years - they had manna (and a few quail).
Still seeking an answer to this question, I found a verse that confused things even more:
Psalm 78:51 (KJV) - 51 And smote all the firstborn in Egypt; the chief (first-fruit) of their strength (power/ability) in the tabernacles of Ham:
How would the evil nature of Ham "hallow" the Israelites? Well, tonight I was watching TCT "Word Pictures" on "Pilgrim's Progress" (Paul Bunyan). Up came a verse I didn't recall reading before so grabbed the Bible for context. Two verses below that one was:
Proverbs 21:18 (KJV) - 18 The wicked shall be a ransom for the righteous, and the transgressor for the upright.
So,the wicked can sanctify? Not possible, to me. Somehow, either Ham (Chm) or Canaan (Knon) had to be the precursor to a Benjamin type. But haven't found the connection yet.