Main Point:
The tree of the knowledge of good and evil is meant to impart knowledge of good and evil through the constant practice necessary to say, “No” to the desire to eat from a tree with tasty fruit.
Minor Point
God never offers instant wisdom in Scripture, but instead treats wisdom as a good to be sought over time. So whatever Adam and Eve receive when their eyes were opened in Genesis was either evil in itself or evil because they were not ready for it.
In my effort to make those two points, things got circuitous.
The Tree
And the LORD God planted a garden in Eden, in the east, and there he put the man whom he had formed. And out of the ground the LORD God made to spring up every tree that is pleasant to the sight and good for food. The tree of life was in the midst of the garden, and the tree of the knowledge of good and evil.
(Genesis 2:8-9 ESV)
Was there really a tree with fruit that conferred knowledge upon its eater? Initially, the idea seems silly. But eating an apple confers knowledge of the taste of an apple. And if you eat a fig and it kills you, your fellow tribesmen know that the fruit is poison. If it does not poison you, you now know a reliable food source. In this sense, knowledge is conferred by the consumption of fruit.
Knowledge of Good and Evil?
But how is it possible that the Bible, which lauds the value of knowledge of good and evil, starts out with a command from God not to eat of a tree which allegedly confers this very knowledge? In Genesis, it appears that God is opposed to the very knowledge that is apparently necessary to please him.
If we read this story in its canonical context, we can see some of what the Biblical authors thought it meant to obtain “knowledge of good and evil.” The Bible is clear that growing in knowledge and wisdom is a process which God intended to take place over time. For instance:
But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.
(Hebrews 5:14 ESV)
And so, from the day we heard, we have not ceased to pray for you, asking that you may be filled with the knowledge of his will in all spiritual wisdom and understanding, so as to walk in a manner worthy of the Lord, fully pleasing to him: bearing fruit in every good work and increasing in the knowledge of God; being strengthened with all power, according to his glorious might, for all endurance and patience with joy; giving thanks to the Father, who has qualified you to share in the inheritance of the saints in light.
(Colossians 1:9-12 ESV)
Maturity of the sort which allows for solid food (explanation of deep knowledge of God) comes from “constant practice” of discerning good from evil. And being filled with knowledge of God’s will is implied to be a process when it leads to “bearing fruit in every good work.” The road of easy knowledge and instant wisdom is a road unknown in Scripture. We know from elsewhere in Scripture that God’s will is that people grow in wisdom over time. We also know that God forbids some things that aren’t intrinsically immoral. An example of this can be found in various dietary and fashion restrictions in the Old Testament. So it’s not knowledge of good and evil that is forbidden. It’s knowledge of good and evil that could result from not eating of the tree.
My thinking is that in Genesis, the tree is named “the tree of the knowledge of good and evil” because having a moral prohibition helps human beings learn moral reasoning, particularly in a world in which things are made to be a hierarchy of goods (Genesis 1). For instance, many things God did not command are morally wrong. God never told anybody not to murder. Yet, Cain’s murder of Abel was immoral and led to punishment.
Similarly, God never commanded anybody to worship, but Cain and Abel innovated sacrifice. In fact, eating meat was neither commanded nor prohibited, Abel did it (as is evident by his sacrifice from his flock) and was not reprimanded. And so it appears that the point of the tree of the knowledge of good and evil was to show that in the hierarchy of goods there are many conflicts and difficulties (it’s wrong to kill humans but not animals), but that explicit rejection of God’s instructions is usually bad (though at times, God has spoken things he apparently did not want obeyed or put into practice at all, see Ezekiel 20:25-26 and Exodus 32).
Possible Corollaries
If what I outlined above is true, it seems that the Bible teaches that Adam and Eve were made innocent, but not perfect. This makes more sense to me. In Genesis 103, it is clear that they are not immortal. They understand death and they also can only obtain immortality by eating from another tree (the tree of life).
This is helpful for general theology/anthropology/theodicy as it is evidence to the effect that God’s purpose in making man was to make a being who would/could grow into moral and spiritual maturity in the face of risks to that process. In other words, the pay off for the possibility of moral development is worth significant potential and actual downsides.
It also helps us understand the fall. A being of perfect righteousness and wisdom would not be able to fall from grace.