The devil was jealous of the bliss of the first people and, in order to deprive them of this bliss, persuaded Eve to taste the forbidden fruit. Eve tasted it and persuaded Adam to do the same.
By breaking God's commandment, Adam and Eve committed sin and were punished for this sin. God expelled them from paradise and condemned them to eternal labor, illness and death.
Having disobeyed the will of God, Adam and Eve, and with them the entire human race, suffered death and fell under the power of the devil.