Why does Paul insist that Christians must give willingly, not as a tax or paying dues?

What is the false prosperity Gospel? How does the sowing and reaping principle in 2 Corinthians 9:6 not lead to a prosperity Gospel?

What will increase your joy in giving?

2 Corinthians 9 ends with a generous God (2 Corinthians 9:15). How does God’s giving inform your giving?