This is a bit different but along the same lines; but learning more and more about the difference between the Old and New Covenant... "It is finished,"
I read this thread and immediately something was quickened to my mind that I had talked about with a group of young men that I am teaching.
When God created man He gave him a certain amount of dominion and authority in the earth. In a sense, man was put in a position of being the "god" of this world as he was given the authority in this world by God. Hebrews 2 and Psalm 8 give us some insight into this, but other verses such as Psalm 115:16, John 10:35 quoting Psalm 82:6, and others. If I have given you a new car, and you decide to drive it over a cliff, I really cannot step in and stop you. I will have violated my own word, something God cannot do. Man willingly gave up this authority and in doing so surrendered to the enemy. So the sacrifice of Christ was necessary. But we read in Romans, Hebrews, and other places that this sacrifice had to be, in a sense, "legal". Since man, flesh and blood, sinned it was only through man, flesh and blood, that this sin could be atoned for. Romans 5 and Hebrews 10 especially. This was the significance of Jesus saying, "But a body thou hast prepared for me," Hebrews 10:5.
Since it had to be "legal", since God could not simply violate His own word and step in without man's consent, there was a covenant made with Abraham. God told Abraham that he was going to have a son, and that this son was going to bring about the seed through which all nations of the earth would be blessed. Paul is very clear in Galatians that this seed is singular, not plural, Christ Jesus Himself. God made covenant with Abraham. If you recall there was the cutting up of the animals, and God appearing as a burning lamp passing between the pieces.
Now if you study covenant, you will realize that it is a very strong thing. If you and I are in covenant, to whatever length you are willing to go for me, I am bound by covenant to go to the same length for you. God, in covenant with Abraham, said, "Take your only begotten son and sacrifice him unto me." Scripture tells us that God did this to test Abraham. But what was He testing?
If we let scripture be commentary on scripture, we find some very interesting things about this testing. Hebrews 11:17-19 tells us that Abraham obeyed God, not weeping over his son, but boldly and in faith with full assurance that if it can down to Isaac dying, God would simply have to raise him from the dead. How did Abraham know this? Because he had already received Isaac from the dead in a figure, or a similitude. Now Jesus said something very interesting to the Pharisees when questioned. Speaking of their father Abraham He said, "Abraham rejoiced to see my day, and he saw it, and was glad." The figure that Abraham saw was the death and resurrection of Christ that God had shown him. The test was whether Abraham would keep his end of the covenant because in doing so he gave God the legal obligation, through covenant, to do THE SAME with His only begotten son. (Really interesting that God called Isaac the only begotten son. Isaac is also called the son of promise.)
So is it just possible that when Jesus said, "It is finished", contained in that statement was, "The covenant that God made with Abraham is completed. The promised seed has given His life just as Abraham offered Isaac. The day that Abraham saw and was glad is here. The thing that was confirmed with Abraham by covenant and revealed to the prophets is completed."?
By the way, remember that Abraham believed and it was counted to him for righteousness? If Abraham saw Jesus day and was glad, what was his faith in? Was it not in the coming messiah, the savior of the world? No wonder this faith was counted for righteousness. It predated the law and put faith in the free gift of the sacrifice of Christ.