Three ways to understand God’s common grace better:
We are no better than those before the flood (8.21, 9.8-17)- the reason God does not flood the earth anymore is not because mankind got “better” but because of God’s gracious promise never to do so again.
Those who are cursed get grace (18-25)- Noah cursed Canaan for what Ham did, but Canaan is still under God’s promise to never flood the earth again.
Those who are blessed still can suffer (26-27)- Shem and Japheth get blessed for their noble actions, but their descendants still experience war and famine and slavery and death throughout history up to the present day.
Why did Noah curse Canaan, the son of Ham? Many commentators have pointed out that this simply follows the pattern of the seed of woman vs. seed of serpent that started in Gen 3.15. Noah is cursing the seed of the serpent!