The forbidden fruit was the knowledge of good and evil. We know that there are two kinds of knowledge, the knowledge that is a product of personal experience and the knowledge that is from being told about something.
I believe that they could not make a decision about the rightness of obeying the command if they had no knowledge about good and evil, ie, no understanding of the goodness of being obedient to the command and the evil of disobedience.
To my mind, they had to have been told about the natural and legal consequences of rebelling against the commandment from GOD to be able to make a truly culpable free will decision to disobey with full mens rea. When they ate they were not making a mistake, they were setting their teeth into a rebellious decision with a full awareness! So what the commandment was doing was warning them to NOT know by experience the knowledge of good and evil, ie, to never choose to rebel and so prove out the consequences.
Eating a biblical metaphor:
From Gen 3:15 On your belly you shall go, And you shall eat dust all the days of your life. eating has been a metaphor for experiencing, especially knowledge and understanding. Do we believe that snakes eat dust? Nothing eats dust so this must be a metaphor for his life.
This metaphor is applied to the law: Psalm 119:103 How sweet are thy words unto my taste! yea, sweeter than honey to my mouth! in which we see eating to refer to his understanding of the great moral strength of the law and its benefits for law keepers.
In Proverbs 9 the call of Wisdom and the seductive lure of Folly's illicit pleasures are both couched in terms of eating:
Wisdom calls:
4 “Whoever is simple, let him turn in here!”
To him who lacks judgment she says:
5 “Come, eat my bread,
and drink the wine I have mixed.
6 Leave your folly behind, and you will live;
walk in the way of understanding.”
Folly calls:
17 “Stolen water is sweet,
and bread eaten in secret is tasty!”
an idea that equates eating with experiencing sin or, if you will, you eat sin and ingest it to become a sinner.
But not just sin.
Jesus refers to our coming to (experiencing) redemption in the same metaphor of experiencing redemption and salvation: John 6:27 Do not work for food that perishes, but for food that endures to eternal life, which the Son of Man will give you.
Isaiah 55:1 "Come, all of you who thirst, come to the waters; and you without money, come, buy, and eat! Come, buy wine and milk, without money and without cost!
The metaphor includes ideas of learning and understanding of doctrine as seen in Ezekiel 2:8 But you, son of man, listen to what I tell you. Do not be rebellious like that rebellious house. Open your mouth and eat what I give you.” 9 Then I looked and saw a hand reaching out to me, and in it was a scroll, 10 which He unrolled before me. And written on the front and back of it were words of lamentation, mourning, and woe.
3:1-4 "Son of man," He said to me, "eat and fill your stomach with this scroll I am giving you." So I ate, and it was as sweet as honey in my mouth.
Revelation 10:10 I took the little scroll from the angel's hand and ate it. It tasted as sweet as honey in my mouth, but when I had eaten it, my stomach turned sour. as well has the idea of experiencing something.
Revelation 3:20 Here I am! I stand at the door and knock. If anyone hears my voice and opens the door, I will come in and eat with that person, and they with me. might refer to more than sharing food and hints at both learning a new understanding of GOD's unity of faith and experiencing HIS heavenly communion.
