(Read Isaiah 1:16-20)

Not only feel sorrow for the sin committed, but break off the practice. We must be doing, not stand idle. We must be doing the good the Lord our God requires. It is plain that the sacrifices of the law could not atone, even for outward national crimes. But, blessed be God, there is a Fountain opened, in which sinners of every age and rank may be cleansed. Though our sins have been as scarlet and crimson, a deep dye, a double dye, first in the wool of original corruption, and afterwards in the many threads of actual transgression; though we have often dipped into sin, by many backslidings; yet pardoning mercy will take out the stain, Psalm 51:7. They should have all the happiness and comfort they could desire. Life and death, good and evil, are set before us. O Lord, incline all of us to live to thy glory.

For a more detailed summary select the link below.

Isaiah 1 Bible Commentary – Matthew Henry (concise) (christianity.com)

Isaiah 1:18

“Come now, and let’s reason together,” says Yahweh:
    “Though your sins are as scarlet, they shall be as white as snow.
    Though they are red like crimson, they shall be as wool.