What does Isaiah 1:18 mean?
Even amid His condemnation of Israel, the Lord pauses to offer them the opportunity to be made clean in His eyes. If they chose, they could avoid the destruction coming for them.The Lord calls His people to reason together with Him. In Isaiah 1:3, He describes them as lacking the basic understanding that all the good they desire comes from Him. If they did understand this truth, they would not be trying so hard to turn away from the Lord (Isaiah 1:4). He has described their whole being as sick (Isaiah 1:5–6).
Now the Lord tells them to use their mental abilities to come to a rational understanding and see that He is right. When they understand that and agree with Him, change is possible. Their sins have stained their hands (Isaiah 1:15) and hearts red like scarlet. If they will repent and change course, those blood-red stains will become as white as snow.
After acknowledging His own sin with Bathsheba many years earlier, King David desired to be made clean in a similar way. "Purge me with hyssop, and I shall be clean; wash me, and I shall be whiter than snow" (Psalm 51:7).