"Now the serpent was more cunning than any beast of the field which the LORD God had made. And he said to the woman, 'Has God indeed said, "You shall not eat of every tree of the garden"?' And the woman said to the serpent, 'We may eat of the fruit of the trees of the garden; but of the fruit of the tree which is in the midst of the garden, God has said, 'You shall not eat it, nor shall you touch it, lest you die.' Then the serpent said to the woman, 'You will not surely die. For 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.' So 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 with her, and he ate. Then the eyes of both of them were opened, and they knew that they were naked; and they sewed fig leaves together and made themselves coverings" (Gen. 3:1-7).
Let us begin by focusing on "the serpent." What do we know about this creature? Very little in this context other than that he is cunning and able to communicate with humans. Obviously, that fact alone indicates this is no ordinary snake. From other passages, we learn that this is the devil himself (cf. Rev. 12:9; 20:2). Jesus taught in John 8:44 that the devil has been a murderer from the beginning as well as a liar, and such is certainly seen in Genesis 3 & 4. He lied to the woman by telling her the opposite of God's instructions. He asked a question to create doubt in her mind. This was enough to lead her to disobey God's clear prohibition. Satan's first attack was against God's word, and he continues attacking it to this day in numerous ways to create skepticism and promote disobedience. In Genesis 3:4 Satan quoted God but added one word ("not"). Proverbs 30:6 comes to mind - "Do not add to His words, lest He rebuke you, and you be found a liar." The serpent added to God's words, would soon be rebuked, and was most definitely a liar!
Satan's words in Genesis 3:5 are enticing and even true to a large extent, though the woman does not fully comprehend the ramifications of what she is contemplating. The devil presents all three avenues of temptation; he doesn't want to fail! I John 2:16 is helpful here - "For all that is in the world--the lust of the flesh, the lust of the eyes, and the pride of life--is not of the Father but is of the world." First, the woman saw that "the tree was good for food"; this is the lust of the flesh. Second, she saw that "it was pleasant to the eyes"; this is the lust of the eyes. Third, she saw that it was "a tree desirable to make one wise"; this is the pride of life. She gave in to these temptations and partook of the forbidden fruit. Adam was with her and she gave some to him, and he ate also. Immediately their eyes were "opened", but not in the manner they anticipated. They first learned the difference between good and evil through their own guilty experience. They realized their nakedness and sought to clothe themselves to the best of their ability. From I Timothy 2:14 we learn a sad truth about Adam here. Although the woman was deceived by the tempter, he was not. Let that sink in. He knew what the serpent was saying was wrong and he was right there with his wife, yet he did not stop her! He allowed her to do wrong and did so himself also. He failed to lead as he was supposed to on this occasion.
One might rightly ask: "Why was this forbidden fruit created in the first place?" The answer lies in the fact that God desired to create humans as free moral agents. In other words, He wanted them to have the ability to choose to serve Him or choose not to serve Him, if they desired. If there was no prohibited behavior in their world, then anything they could do would always be right. There would have been no way for them to rebel against God or choose not to love Him. God did not want "robots" to serve Him with no choice; He wanted beings with free will to choose to serve Him. Thus, the tree of the knowledge of good and evil was a test of their love. Tragically, they failed the test in a relatively short span of time it would seem, and they had no excuse. They allowed an animal to persuade them to break the commandment of Almighty God! They were to exercise dominion over the beasts, not get instructions from them!