The Tree of the Knowledge of Good and Evil is a meaningful symbol in the Bible: When Eve ate its forbidden fruit and gave it to Adam it signaled the fall of mankind. But beyond simple disobedience, why was it so significant, and why was the outcome so drastic? The Tree of Knowledge represents spiritual thinking that is based on our human senses and intelligence -- things we figure out for ourselves instead of getting from the Lord. That might not sound like such a bad thing, and to some extent it's not for us in the modern age. But the people represented by Adam and Eve were celestial, which means they were in a state of love to the Lord and received wisdom from Him directly. From the love they felt they knew instantly what was right and true and what was wrong and false. But on some level they wanted to live from themselves, not from the Lord, and started pushing away the Lord's leading and trusting in their own intelligence instead symbolized by eating of the Tree of Knowledge.

In Genesis 6:5, this signifies no will for good, and so no perception of good and truth. (Arcana Coelestia 586)

In Psalm 7:4, this signifies that the Lord is justice, and there is no evil in Him. (The Inner Meaning of the Prophets and Psalms 257)

In Genesis 19:19, this signifies the danger of being at the same time in evil and good. (Arcana Coelestia 2426)

In Matthew 6:13, evil is rejected by the angels until only good remains with no idea of evil; and this with a kind of indignation that evil should be thought of when the Lord is thought of. (Arcana Coelestia 3605[2])

In Isaiah 5:20, this signifies that the distinction should be acknowledged. (Apocalypse Explained 526[7])