Isa 1:18, Heb 9:13-14,19-22, 1 Jn 1:7
In the Old Testament, David admitted that he was a sinner and asked God to wash away his sins. (Psalms 51:7)
Psalms 51:7 Purge me with hyssop, and I shall be clean: wash me, and I shall be whiter than snow.
The Old Testament prophesied that God would wash away our sins. (Isa 1:18)
Isa 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.
Jesus, the Christ, shed His blood to wash away our sins. (Hebrews 9:13-14, 19-22, 1 John 1:7)
Hebrews 9:13 For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh: 14 How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God? 19 For when Moses had spoken every precept to all the people according to the law, he took the blood of calves and of goats, with water, and scarlet wool, and hyssop, and sprinkled both the book, and all the people, 20 Saying, This is the blood of the testament which God hath enjoined unto you. 21 Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry. 22 And almost all things are by the law purged with blood; and without shedding of blood is no remission.
1 John 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.