[Heb 13:20 KJV] 20 Now the God of peace, that brought again from the dead our Lord Jesus, that great shepherd of the sheep, through the blood of the everlasting covenant,You were talking about the new testament not being in force until Jesus died.
It is actually his new covenant that required his death,blood,to seal the covenant. Which transpired when he died on the cross. That is the meaning of our sins being "under the blood".
They are erased by his sacrifice for our sins. That propitiation for our sins.
After he died on the cross and forever his new covenant is in force.
And the new testimony in our Bibles tells us why that is the truth.