God acts on the principles which define His very character: justice, love, power, and wisdom. The Psalmist says in Psalm 89:14 “Justice and judgment are the habitation of thy throne: mercy and truth shall go before thy face”. The foundation of God’s law is justice. Justice operates with mercy, but justice must also be met.
When Adam and Eve disobeyed God, justice required they receive the stated punishment: “but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die,” Genesis 2:17 (NKVJ).* Adam and Eve were barred from the Garden, and the consequences of sin and death were passed on to all of their children.
God could not violate his own law. God “cannot deny Himself,” 2 Timothy 2:13. He had to carry out the sentence. Yet even while exercising justice, He offered a glimpse of hope. He promised that the woman’s seed will one day bruise the serpent’s head. This is the key principle of God’s salvation: God created a plan to satisfy justice and still allow love to operate. The redemption of Adam and his children would be achieved by the willing sacrifice of his only begotten Son.
Paul explains that God is demonstrating “at the present time His righteousness, that He might be just and the justifier of the one who has faith in Jesus,” Romans 3:26 (NKJV). By his sacrifice, Jesus satisfied divine justice and offers all an opportunity to gain eternal life. Some will receive salvation now, while the majority of mankind will be restored in the Millennium. Revelation 22:1-2 (NKJV), “he showed me a pure river of water of life, clear as crystal, proceeding from the throne of God and of the Lamb. In the middle of its street, and on either side of the river, was the tree of life…The leaves of the tree were for the healing of the nations.”
God’s divine plan for mankind is a demonstration of his character. He was just and yet found a way to demonstrate the deepest love and mercy ever beheld in the history of the universe. Mankind’s experience with evil will be an eternal lesson for all creatures and will never need to be repeated.
* Please see the question: “God can't lie. But He instructed Adam that he would surely die in the day he disobeyed. However, Adam lived 930 years before he died!”