Father's perfect will and His allowed will...

This is a two part question:

1. How do you know the difference between Father's perfect will and his allowed will as there is I can see a distinction between the two in Scripture?

An example: marriage - Father's perfect will in Gen 2:24 is that there shouldn't be any divorce, but in Deut 24:1 the "adendum" law is given about divorce. (This is just a quick example and it is a much bigger study.)

2. Which "will" should we strive to keep in our own walk; Father's perfect will and His allowed will?