Leviticus 11 deals with clean and unclean animals. I don't know why God chose some animals to be clean and some to be unclean, but I think that's the point.
Animals are clean or unclean because God says so. Sin is sin because God says so. We do not get to determine what is sin and what is not - that is for God alone. He is holy and He is God, so what He says goes. If my opinion differs from His, I am wrong, every single time.
Leviticus 12 deals with uncleanness due to childbirth. Of course, the first question is why is there double the time for girl babies as there is for boy babies. I read up on it a little bit and found a few opinions that make sense to me.
First, the whole point of being unclean due to childbirth is to remind us of the origin of sin - we are born into it. We aren't sinners because we sin. We sin because we are sinners, right from birth. Here, the woman was symbolically responsible for bringing another sinner into the world. And, when giving birth to a female, the woman gives birth to a sinner who will give birth to more sinners, hence the longer period of uncleanness.
Another theory is that it is a reminder of the fall of man, and the specific curse on the woman and childbirth.
One good thing about these periods of uncleanness is that it gave the new mother a time of rest and seclusion that would be welcomed. In the case of a girl baby (which was likely a bit of a disappointment, simply due to the culture at the time) it gave more time to bond more deeply with the newborn girl.
The book of Hebrews ties in very well with the book of Leviticus. Our passage today specifically speaks about the sacrificially system being needed year after year because it didn't take away sin, it pointed to Jesus who is the Perfect Sacrifice, and who is the only One who can make us clean.
This past Easter weekend we celebrated exactly that.
Jesus' job of being the perfect sacrifice is done! And He signified that it was done by sitting down at the right hand of God.
And when Jesus died, He dealt a deathblow to His enemies - over Satan and all the fallen angels, and over all who reject Him. Death is Satan's greatest weapon, and Jesus completely destroyed it.
It was a one time act, and it was the most magnificent masterpiece of all time.
Tomorrow's Bible In a Year Passage passage: Leviticus 13; Hebrews 10:19-39