One of the explanations when I was first coming to understand why Jesus' sacrifice was necessary was something along the lines of: Sin separates us from God. God can not be around sinners, so with Jesus' sacrifice wiping away our sin, we can be with God once more.

But if God cannot be around sin, how is it that Satan was able to go before him in the book of Job ?

6 One day the angels came to present themselves before the LORD, and Satan also came with them.