Isaiah 1:18

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" (Mat 27:28). So Rahab's thread (Jos 2:18; compare Lev 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-- (Psa 51:7). Repentance is presupposed, before sin can be made white as snow (Isa 1:19-20); it too is God's gift (Jer 31:18, end; Lam 5:21; Act 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).

— Jamieson-Fausset-Brown Commentary (public domain)