John Calvin Commentary Genesis 3:5

"for God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as God, knowing good and evil." — Genesis 3:5 (ASV)

For God does know. Some think that God is here craftily praised by Satan, as if He would never prohibit people from using wholesome fruit. But they clearly contradict themselves, for at the same time they confess that in the preceding part of the sentence, Satan had already declared God to be unworthy of trust, as one who had lied.

Others suppose that Satan charges God with malice and envy, as wishing to deprive humanity of its highest perfection; this opinion is more probable than the former. Nevertheless, (in my judgment) Satan attempts to prove what he had recently asserted by reasoning from opposites: he argues that God has forbidden you the tree so that He might not be compelled to admit you to share in His glory. Therefore, the fear of punishment is quite needless.

In short, Satan denies that a fruit which is useful and beneficial can be harmful. When he says, God does know, he criticizes God as being motivated by jealousy, and as having given the command concerning the tree for the purpose of keeping humanity in an inferior rank.

You shall be as gods. Some translate this as, ‘You shall be like angels.’ It might even be rendered in the singular: ‘You shall be as God.’

I have no doubt that Satan promises them divinity; as if he had said, “God deprives you of the tree of knowledge for no other reason than because He fears having you as companions.”

Moreover, it is not without some semblance of reason that Satan makes divine glory, or equality with God, consist in the perfect knowledge of good and evil; but this is a mere pretense, designed to ensnare the unfortunate woman.

For the desire for knowledge is naturally inherent in us, and happiness is often thought to be found in it. However, Eve erred by not regulating the extent of her knowledge according to the will of God.

And we all daily suffer from the same affliction, because we desire to know more than is right and more than God allows; whereas the principal point of wisdom is well-ordered self-control in obedience to God.