There is also a mystery of iniquity. There is a mystery of Babylon the Great. This is the institutional system of iniquity, of the prostitution of the spiritual principles and truth of God's grace. The mystery of iniquity is able to exist by taking advantage of the mystery of grace. The central way in which it is able to do this is by insinuating that God's grace is just natural. It can be taken for granted. It can be counted on no matter what, just by nature.
The serpent started this insinuation in the Garden of Eden. Eve let it be known that she feared to even touch the Tree of the Knowledge of Good and Evil because God said to Adam that in the day they ate of its fruit they would die and it would be absolute death. The serpent questioned this. Subtly, the serpent at first insinuated that God did not really mean what He said literally. Then the serpent came out and said directly that what God said would happen would not literally happen. Why? Well, the insinuation was that God's grace would prove to be an integral part of nature.
The serpent attempted to get Eve to believe that however the threat of death was to be perceived she could count on it not to be the end of her. She could count on the grace of God. This is the inception of the mystery of iniquity.
Cain listened to this insinuation of the serpent. Abel did not. Cain began to think and act like a measure of reformation from his parent's rebellion against God would be enough. The grace of God could be counted on to under-gird creation itself. Abel did not believe this. Abel believed that God's word was immutable. He believed that complete and absolute death was indeed the consequence of sin. From this, he saw that a willingness to reform behavior, by itself, would not constitute true repentance. The only hope of God's grace would be through God's undeserved mercy resulting in a resurrection from the dead.
God received Abel's sacrifice of an animal showing his hope in God's mercy and faith in God to raise the dead, should God choose to be gracious. God did not receive Cain's sacrifice of grain, by which Cain indicated that he believed God was only looking for signs of reformation, because God's graciousness could be taken for granted and it could be taken for granted that God would not destroy the world.
Then, seeing God's approval of his brother's sacrifice, Cain killed Abel. This was the onset of the institution of the mystery of iniquity. It was upon this principle of hatred toward those who believe God's word that the final institution of the mystery of iniquity, Babylon the Great, would be built. For it would not only be that Babylon would take Judah into captivity, it would be this institution of the mystery of iniquity that would take the faith of Israel, which was the hope of Abel, into captivity and would not let it go, until finally this mystery of iniquity would be destroyed by the Revelation of the Mashiach of Israel, who is the one who reveals the mystery of the grace of God in truth.