What is the knowledge of good and evil? It is knowing...
-> what choices lead to ¹life
and
-> what choices lead to ²death
³Without God we do not (and can not) know with absolute certainty - especially in the more critical decisions - which is which (we are finite), we only think we know.
Decisions we believe lead to life often lead to harm and destruction. And decisions that result in pain aren't always bad but can ultimately lead to life (e.g. "no pain, no gain"). Knowledge of good and evil is not as obvious or black and white as we might think.
The serpents promise to Eve was once you eat of the tree you would have ⁵the knowledge of good and evil i.e. you don't need God for this. The tree (creation) will give you this without depending on God.
This was a lie. Only God alone is all-knowing and all-wise. Only He knows what is best not us.
We must look to Him to get "it" right. We bristle at this. But this reveals the depth of our rebellion to and distrust of God if we are honest.
Our original parents abandoned the reality of their dependence on God and sought to be their own god. All of us have continued on the same path since. The result was the pain and suffering we see today and have throughout human history.
It should be very clear that humanity is not capable of being their own god and making the best choices on their own. Thinking they could know good and evil without God didn't work out as well as the serpent suggested. But instead, as God warned i.e. it lead to death.
We think we can know which choices bring ¹life or death without depending on God's input, when the reality is our independent choices can, and often do, lead to death, the exact opposite of life.
We think we are gaining life through our independent pursuits - pursuits of created things or persons over our pursuit of God (who made all things) - when we are actually choosing the opposite i.e. that which ultimately results in our harm, destruction and death.
While created things are good, not evil and necessary and worth pursuing, they are simply not the Creator. They will never fulfill the expectations we put on them because they (we) were not designed to. Only the Creator can meet our deepest and greatest needs and longings, not creation.
Creation is only a means to life not the source. God is the Source of life, love, and all created things.
What about the tree of life?
The reason Adam and Eve were banned from access to the tree of life is by having access in their state of rebellious distrust it would allow them to continue on with the lie that they could find life on their own in and through creation (i.e. the fruit from the tree of life) and not in or through God the only wise Creator. Believing they could, was the result of them already buying into the lie that they could sustain life outside of or apart from God by eating from the tree of the knowledge of good and evil.
In other words to continue living without ever dying, we would only need to eat from the tree of life, thinking it was the source of life, instead of God - who alone is true and lasting life. Trees are great but they are still only trees.
Having access to the tree of life would allow them to continue on in the lie that created things are the ⁵source of life. This would allow us to continue our life independent of God; or so we think. It would ultimately result in harm, destruction, and death, not true life, because only God is our source, not trees (i.e. not created things).
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¹True and lasting life as we were designed to experience it is not short-term life. True life is eternal and infinite vs temporary and limited. As bearers of God's image we must have infinite life to flourish and be all we are designed to be, not the fleeting life we gain in and through creation.
²Death comes by the absence of God and anything that separates us from Him and His presence. This isn't just physical death but spiritual death which is the absence of God's presence.
³Before Adam and Eve ate, they didn't need to know, they only needed to trust that God knew and that should have been enough. To this day we rebel against this notion that God knows better than us.
Knowing good and evil is good not bad. It is a quality that God himself possesses. So it can't be bad. The problem is it is not a quality we can obtain on our own, apart from God.
Knowing good and evil or trying to determine it on our own instead of seeking God to reveal to us what is best comes up short and ultimately leads to death, as God warned.
So why shouldn't we also have this knowledge? We can.
Thinking we could determine good and evil without God's aid or direction is our problem. Not having knowledge of it.
Why?
Only God is all knowing and infinite. We are not.
If Adam and Eve had fully trusted God and obeyed by not eating of the forbidden tree would have been the first step in knowing right from wrong but under God's direction not independent of God. Trusting God would have lead them ⁴to a true understanding of good and evil. God alone fully understands good and evil and we must always depend on Him to know what is best.
⁵The knowledge of good and evil indicates knowledge of good and evil is not bad in itself. However having true knowledge is only possible with God not us. In order to have this knowledge requires dependence on God for He alone has it perfectly.