What was the essence of the lie that Satan, the deceiver, spoke to Eve?
For God knows that in the day you eat from it your eyes will be opened, and you will be like God, knowing good and evil. Genesis 3:5
First, let’s consider what it’s not. The lie was not found in their being like God. The truth is that they were already like God, for they had been made in his image. This is in no way a setup for man to be in competition with God, but that man’s very being was to express the nature of God in the creation. Their being made in the image of God was the amazing reality that the liar set out to discredit. In other words, their very beings were defined by the creator himself. But when the serpent approached Eve with the proposition that they would be like God by eating the forbidden fruit, he was speaking a lie. It was a lie because it totally undermined the truth of their inherent likeness to God. The serpent basically made the demand that they were not like God, but that they could be, if they took it upon themselves —as beings who were separate from God— in eating the fruit God forbade.
The irony in Satan’s lie was that Adam and Eve became unlike God when they did the thing he said would make them like God. The same deception comes at us to this day. We have been made alive to God in Christ. We have been brought into union with God through Jesus Christ. We have been made partakers of the divine nature. Our union with the father through Christ is so amazing that Paul said that he no longer lived, but Christ lived in him. Jesus said that we would be made one, even as he and his father were one.