Hebrews 9:22 And almost all things are by the law purged with blood; and without shedding of blood is no remission.
Their blotting out of sins is at the second coming of the Lord
Acts 3:19 Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord.
Acts 3:20 And he shall send Jesus Christ, which before was preached unto you:
Acts 3:21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
Paul confirms it.
Romans 11:26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:
Romans 11:27 For this is my covenant unto them, when I shall take away their sins.
Whereas we in the Body have now received the atonement.
Romans 5:11 And not only so, but we also joy in God through our Lord Jesus Christ, by whom we have now received the atonement.
It's as simple to understand as: They look forward to that day (Zechariah 13:1 KJV, 1 John 1:9 KJV while we look back to the cross Colossians 2:13 KJV).