A fine question. And that's why the text is a messianic prophecy and a proof that no future messiah has come yet. You should reread that section. It explicitly states how it is going to work. Now, whether people will be "sinless" is a matter of understanding. There will still be certain sins in the future, and pure/impure.
This is the theology you abide by. I don't agree to your underlying assumptions.
As shown, textually and theologically not true. You start with this as your contention and have to misread text to interpolate blood where there is none.
Really? Ask Miriam.
If blood did the job, why did people have to be "repentant"?
Yes, for dinner, not for atonement. They ate it. It had nothing to do with sins.
I'm in New Jersey. Can you be delivered from ignorance while you cling to misunderstandings?
The blood of an unblemished lamb was painted around the doors of the Hebrew houses in Egypt. The effect was to prevent the angel of death, the destroyer, from taking life.
Exodus 12:13; 'And the blood shall be to you for a token upon the houses where you
are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you, when I smite the land of Egypt.'
Exodus 12:23;'For the LORD will pass through to smite the Egyptians; and when he seeth the blood on upon the lintel, and on the two side posts, the LORD will pass over the door, and will not suffer the destroyer to come in unto your houses to smite
you.'
So, it wasn't just a case of sitting down for a lamb chop before heading off to the desert!
There is also no foundation to the idea that repentance replaces the need for blood. The once-for-all-time atoning blood is poured out by God Himself as a payment for sin. We sinners must still be repentant if we are to receive the forgiveness that comes from faith in his atoning blood.
As John the Baptist said, 'I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and
with fire:' [Matthew 3:11]
What this tells us is that we must repent
and believe in the atoning sacrifice of Christ, because only through resurrection from the dead, and ascension to heaven is the giving of the Holy Spirit made possible.
On the day of Pentecost, following the resurrection, we have this [Acts 2:38], 'Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of Holy Ghost.'
It is necessary to repent AND have faith in Christ.