There was nothing inherently magical, different or evil about it. Eve saw that it was good for food and beautiful to see (Gen 3:6). It probably was very similar to or the same kind as the tree of life near or next to it (Gen 2:9, 3:3) - Don't forget, God said all the trees were good for food (Gen 1:12; 2:9, 16-17).
The main purpose of the tree of the knowledge of good and evil didn't lie within the tree itself.
The primary purpose of the forbidden tree was to see whether Adam and Eve (and now we) would follow God's direction as instructed i.e. would they trust God and follow His directions or not.
The fear of the Lord (perfect regard and respect for God and His directions/instructions) is the beginning of wisdom. Wisdom = true understanding of right from wrong. If Adam and Eve had listened to God's direction - i.e. had proper regard for Him and respected His direction to not eat - they would have taken the first step onto the road of true wisdom and understanding of right from wrong - good and evil - the right way i.e. by following God's direction and not trying to gain this knowledge on their own i.e. through their independent (rebellious) efforts of taking it against God's instructions.
To gain the knowledge of good and evil the right way was by trusting God and His word (His warning) and acting accordingly. To believe (trust) God even if His word didn't make sense (the tree looked good for food, so what's the problem in eating from it) regarding the direction He gave or circumstance(s) He allowed. We are to still trust God - believe He's good and desires our good - no matter what we encounter or how little it make sense.
The primary purpose of the forbidden tree was to see whether Adam and Eve (and now we) would follow God's direction as instructed i.e. would they trust God and follow His directions or not.
The fear of the Lord (perfect regard and respect for God and His directions/instructions) is the beginning of wisdom. Wisdom = true understanding of right from wrong. If Adam and Eve had listened to God's direction - i.e. had proper regard for Him and respected His direction to not eat - they would have taken the first step onto the road of true wisdom and understanding of right from wrong - good and evil - the right way i.e. by following God's direction and not trying to gain this knowledge on their own i.e. through their independent (rebellious) efforts of taking it against God's instructions.
To gain the knowledge of good and evil the right way was by trusting God and His word (His warning) and acting accordingly. To believe (trust) God even if His word didn't make sense (the tree looked good for food, so what's the problem in eating from it) regarding the direction He gave or circumstance(s) He allowed. We are to still trust God - believe He's good and desires our good - no matter what we encounter or how little it make sense.
This is our struggle to this day (we are walking in the same footsteps of our original parents - or ancestors if you wish). We either believe God is good in any and every given circumstance and situation or we don't.
The purpose of the tree was to simply test whether they trusted God or not. It was a test of whether they recognized their total dependence on God for true life and wisdom or believed they could somehow find it on their own - be their own god - and make life work without Him.
They choose to believe the lie that they could gain wisdom - and thereby life - without God by means of the forbidden tree.
The tree was forbidden so they might acquire wisdom the right way i.e. through obedience to God's direction.
They rebelled and rejected His direction and instructions. They did not trust God but suspected He was holding out on them (as the serpent suggested), so they turned away from Him and to created things instead for life e.g the forbidden tree, each other, and their own understanding. As a result they experienced just the opposite - death - exactly as God warned.
We do this today as well and continue to wrestle with our obedience to God daily.
Only by faith in His love for us - proven by Christ bearing the consequences of our rebellious disobedience - are we empowered to live for Him. Sending Christ to restore us - by living the life of obedience, we should have lived and suffering the consequences of disobedience that we should have suffered - is proof on a infinitely grand scale that God loves us and wants what is best for us, even in our rebellious distrust.
"The just (righteous) shall live by faith" is quoted in 4 different places in scripture for an important reason. God wants to be sure we "get it." It is the means by which we partake of and participate in the gospel - the "good news." We not only enter into God's kingdom by it, but we live out His kingdom daily through it.
For a discussion on the gospel of the kingdom, click here