That by this alone the Jews can receive pardon of their sins, if they wash away the blood of Christ slain, in His baptism, and, passing over into His Church, obey His precepts
In Isaiah the Lord says: “Now I will not release your sins. When you stretch forth your hands, I will turn away my face from you; and if you multiply prayers, I will not hear you: for your hands are full of blood. Wash you, make you clean; take away the wickedness from your souls from the sight of my eyes; cease from your wickedness; learn to do good; seek judgment; keep him who suffers wrong; judge for the orphan, and justify the widow. And come, let us reason together, says the Lord: and although your sins be as scarlet, I will whiten them as snow; and although they were as crimson, I will whiten them as wool. And if you be willing and listen to me, you shall eat of the good of the land; but if you be unwilling, and will not hear me, the sword shall consume you; for the mouth of the Lord has spoken these things.”
Source: The Treatises of Cyprian (New Advent)