This is a weighty chapter. Surprise, surprise.
One takeaway is the difference between God ordaining evil, and God permitting Evil. Piper says it this way:
By ordain I mean that God either caused something directly or permitted it for wise purposes. This permitting is a kind of indirect causing, since God knows all the factors involved and what effects they will have and he could prevent any outcome. So his permission is a kind of secondary causing, but not a direct causing.
This distinction is an effort to be faithful to the different ways the Bible speaks about God's relation to events.
So God secondarily or indirectly causes evil. But even when he does permit evil, it is with a purpose. Whether by causing or permitting, God directs events to glorify Christ.
God planned to use the sin of Adam before Adam had committed the sin. Piper says:
For example, in Revelation 13:8, John writes about "everyone whose name has not been written before the foundation of the world in the book of life of the Lamb who was slain." So there was a book before the foundation of the world called "the book of life of the Lamb who was slain." Before the world was created, God had already planned that his Son would be slain like a lamb to save all those who are written in the book.
When Adam sins, God does not go to his back-up plan. He knows it will happen and continues with his plan to glorify Christ by saving those whose names are written in "the book of the life of the lamb who was slain".
The last main takeaway for me in this chapter was the explanation of Adam as a "type" of Christ. The following paragraph explains it well:
Here's the parallel: People whose transgression was not like Adam's died like Adam. Why? Because they were connected to Adam. He was the representative head of their humanity, and his sin is counted as their sin because of their connection with him. That's the essence of why Adam is called a type of Christ—because our obedience is not like Christ's obedience and yet we have eternal life with Christ. Why? Because we are connected to Christ by faith. He is the representative head of the new humanity, and his righteousness is counted as our righteousness because of our connection with him (Rom. 6:5).
That's the parallel implied in calling Adam a type of Christ:
Adam >Adam's sin >humanity condemned in him >eternal death
Christ >Christ's righteousness >new humanity justified in him >eternal life
And this passage is universal. Every single human you meet is either under Adam, and condemned in sin, or justified and alive in Christ. This is not a wimpy worldview. But wimpy worldview's create wimpy Christians.
