God called his people to come and settle their dispute so that he could restore his covenant relationship with them. Judah had to choose between obedience and rebellion (Isaiah 1:19–20). Isaiah says their sins are "like scarlet" and "red like crimson," the color of blood, which Judah had shed unjustly (Isaiah 1:15).
white as snow … like wool: The people would be radically transformed. God would cleanse, purify, and make them holy (see also Psalm 51:7; Daniel 7:9).