Bible commentators say that scarlet portrays sin, not only to denote its dreadful character, but also to emphasize its indelible nature. They tell us that you can immerse a cloth in any other color and the stain can be removed. Once red dye has been thoroughly set in a piece of goods, however, no scientific method is know that can successfully eliminate it without damaging the fabric. Even if the material is rubbed and scrubbed until threadbare, the fibers that are left will still retain their crimson hue.
Sin is thus pictured as being indelible as far as human efforts to remove it are concerned. There is nothing man himself can do to change his evil nature and turn it into the white purity of holiness. God alone has the power to erase the terrible stain of our sin.