We're only sons/daughters of God through faith, BECAUSE Jesus was without sin, and could make it possible for us to become sons and daughters.
My sin-filled state prevents me from being able to make an acceptable sacrifice.
According to the law, those who sin shall die.
Romans 6:23 says that the wages of sin is death.
So, my sin kills me, and makes me incapable of making an offering for my sin. According to the Law, I'd have to offer the life of an animal, upon whom I could pass my sin.
Once Jesus became God's Lamb who took away the sin of the world, no other offerings or sacrifices for sin are valid.
This is more fully described in the new testament letter to the Hebrews.
Hebrews 10 - For the law, having a shadow of the good things to come, [and] not the very image of the things, can never with these same sacrifices, which they offer continually year by year, make those who approach perfect.
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Because it was always the sacrifice of another which had to be done.
Sin results the death of the person who commits the sin.
the levitical law made provision for receiving forgiveness, and cleansing.
Once Jesus came, that was all fulfilled in Jesus. Now, there is no more offerings or sacrifices for sin. Jesus was it.