Adam was the first man created by God. He was the representative of all men going forward in human history. God gave Adam instructions to enjoy the Garden of Eden that God created. But Adam had only one condition that God gave to him. He was not to eat of the “tree of knowledge of good and evil.”
“15Then the Lord God took the man and put him in the garden of Eden to tend and keep it. 16And the Lord God commanded the man, saying, ‘Of every tree of the garden you may freely eat; 17but 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.’” (Gen. 2:15-17).
But the serpent deceived Eve and she ate the forbidden fruit of the tree. She also gave its fruit to Adam and he ate it. Thus the sinfulness of man was manifested for all mankind throughout human history.
“4Then the serpent said to the woman (Eve), “You will not surely die. 5For God knows that in the day you eat of it your eyes will be opened, and you will be like God, knowing good and evil.” 6So when the woman saw that the tree was good for food, that it was pleasant to the eyes, and a tree desirable to make one wise, she took of its fruit and ate. She also gave to her husband (Adam) with her, and HE ATE.” (Gen. 3:4-6).
Adam was the federal head of mankind, as Jesus Christ is the federal head of the redeemed. Adam possessed all that was necessary to continue without falling, yet he fell. He disobeyed God. Thus spiritual and physical death and condemnation under sin to eternal death in the Lake of Fire passed on to all humans since Adam was the Federal head and all of his offspring are born spiritually separated from God with a sinful nature in slavery to sin, and all sin (Rom. 5:12).
“12Therefore, just as through one man (Adam) sin entered the world, and death through sin, and thus DEATH SPREAD TO ALL, MEN, BECAUSE ALL SINNED.” (Romans 5:12).
“10As it is written: ‘There is NONE RIGHTEOUS, NO, NOT ONE; 11there is none who understands; there is NONE WHO SEEKS AFTER GOD. 12They have ALL turned aside; they have together become unprofitable; THERE IS NONE WHO DOES GOOD, NO, NOT ONE.’” (Romans 3:10-12).
The good news is that because of Jesus Christ and His righteous atonement, justification of life by faith in Christ has come as a free gift for all who put their faith in Him.
“18Therefore, as through one man’s (Adam) offense JUDGMENT CAME TO ALL MEN, RESULTING IN CONDEMNATION, even so through one Man’s (Christ) righteous act the free gift came to all (elect) men, resulting in JUSTIFICATION OF LIFE.” (Romans 5:18). (See: Isaiah 53:12; Matt. 1:21; 26:28; Mark 13:20; John 1:12; Titus 1:1; Heb. 9:28; 1 Pet. 1:2).
[For a more in-depth study see eschatology “Study Series 3 What Happened in the Garden”]