Through man's fall, man let sin enter into him. Romans 5:12a says that through one man sin entered into the world. Actually the world here means mankind. When sin entered into man, that really meant that Satan entered into man.
The real significance of man's fall is that Satan was taken into man, sin entered into man, and man became a victim of death (Rom. 5:12b, 14a; 1 Cor. 15:22a). Romans 5:12b points out that through sin entering into the world, death passed on to all men. Death is the ultimate result of man's fall. Romans 5:14a says that from Adam to Moses, death reigned. Death even became a king. First Corinthians 15:22a says that in Adam all die. Thus, all of mankind is a victim of death through man's fall.
In this lesson we have to stress how man became one with Satan in his three parts. Every part of man was ruined, corrupted, and deadened, making man a hopeless case. Sin entered into man, moving, damaging, and killing man, and man is now altogether under the tyranny of death. Man is a victim of death. It is not just man transgressing against God, not just man falling under God's condemnation, but man receiving Satan into himself. Satan's being entered into man's being, and Satan himself as sin entered into man's body, making man's body the flesh. Through all this, man's spirit was also deadened.
We must make all these points so clear and so impressive to the saints. Then we can go on to help the saints to see the need of life. There is not just the need of an objective salvation, but the need of a subjective life. Lesson four and this lesson are crucial so that we can have the proper experience of life.
We must do a good work to make all the saints clear about how Satan spoiled man and how man fell. It is not just a matter of man transgressing against God and falling under God's condemnation, but a matter of man taking in something. We may use the illustration of a mother warning her child not to take in something poisonous. This is the mother's commandment. If the mother leaves home and the child takes in that poison, this is not merely a transgression against the mother's commandment. It is a receiving of the poison into the child's being. This is an illustration of what happened when man fell. When God comes in to save us, He does not just take care of our transgression and of our being under His condemnation. He also works to take away the poison and to rescue us from death.