isaiah 1:18 Come now, and let us reason together, saith the LORD: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool. - Free Bible Online

      18. God deigns to argue the case with us, that all may see the just, nay, loving principle of His dealings with men (Isa 43:26).
      scarlet--the color of Jesus Christ's robe when bearing our "sins" (Mt 27:28). So Rahab's thread (Jos 2:18; compare Le 14:4). The rabbins say that when the lot used to be taken, a scarlet fillet was bound on the scapegoat's head, and after the high priest had confessed his and the people's sins over it, the fillet became white: the miracle ceased, according to them, forty years before the destruction of Jerusalem, that is, exactly when Jesus Christ was crucified; a remarkable admission of adversaries. Hebrew for "scarlet" radically means double-dyed; so the deep-fixed permanency of sin in the heart, which no mere tears can wash away.
      snow-- (Ps 51:7). Repentance is presupposed, before sin can be made white as snow (Isa 1:19, 20); it too is God's gift (Lamentations+5:21,Acts+5:31">Jer 31:18, end; La 5:21; Ac 5:31).
      red--refers to "blood" (Isa 1:15).
      as wool--restored to its original undyed whiteness. This verse shows that the old fathers did not look only for transitory promises (Article VII, Book of Common Prayer). For sins of ignorance, and such like, alone had trespass offerings appointed for them; greater guilt therefore needed a greater sacrifice, for, "without shedding of blood there was no remission"; but none such was appointed, and yet forgiveness was promised and expected; therefore spiritual Jews must have looked for the One Mediator of both Old Testament and New Testament, though dimly understood.

JFB.