Why was Lucifer not locked up immediately after he revolted against God in heaven? Why was he cast down with his fallen angels who are now principalities and powers of darkness? (Isa. 14:12) What is Satan doing on our planet? Why did God not intervene when the serpent was deceiving Eve? Why did God not stop Adam and Eve from eating the forbidden fruit? The answer is very simple. God made man as a free moral agent who can exercise his will power to make choices. God will allow man to choose, but there shall be consequences for the choices we make. This is the grand design of our loving creator. The power of choice was given to us by God. This is what distinguishes humans from other animals. Fortunately, God allows for a chance of redemption for the sins we commit on earth. But he did not allow for a chance of redemption for the sins that the angels committed in heaven. The angels have more light, were closer to God and have better knowledge hence, no chances and no trial period.
God told Adam and Eve that the day they eat of the fruit of the tree of knowledge, they shall surely die. When the serpent came, he said to Eve: "you shall not surely die" (Gen. 3:4). The trick here is that there are two kinds of death. Spiritual death is eternal separation from God. That is the real death. Physical death is just a transition from one level of existence to the other. What God said was that they will die spiritually if they eat that fruit. What Satan meant was that they will not die physically. Satan was right in a way because Adam lived for 930 years in the flesh after eating that fruit, but Satan lied because he intentionally misled Eve by focusing on the physical aspect of death rather than the spiritual aspect which was God's intended meaning. The fact remains that Adam and Eve died spiritually the very day they ate the forbidden fruit. "But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die." (Gen. 2:17) But God gave us a way out, a plan of redemption was revealed after Adam and Eve sinned. Jesus Christ is the lamb slain from the foundation of the world. (Rev. 13:8)