God created the world perfectly and did not screw anything up. However, with a perfect world came the responsibility and the commandment to keep it that way:
9 And the LORD God made
all kinds of trees grow out of the ground-trees that were pleasing to the eye
and good for food. In the middle of the garden were the tree of life and the tree of the
knowledge of good and evil.
10 A river watering the garden flowed from
15 The LORD God took the man and put him in the Garden of Eden to work it and take care of it. 16 And the LORD God commanded the man, "You are free to eat from any tree in the garden; 17 but you must not eat from the tree of the knowledge of good and evil, for when you eat of it you will surely die."
There was only one tree that they could not eat from: “tree of the knowledge of good and evil”. They were free to eat from the tree of life. Therefore, they would have lived forever, since there was no death, sickness, or any problems at all.
Genesis Chapter 3 describes the original sin of mankind. Its immediate effect on all the humans of the world, and their descendents was this: It brought death:
They could no longer eat of the tree of life:
22 And the LORD God said, "The man has now become like one of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever." 23 So the LORD God banished him from the Garden of Eden to work the ground from which he had been taken. 24 After he drove the man out, he placed on the east side  of the Garden of Eden cherubim and a flaming sword flashing back and forth to guard the way to the tree of life.
This introduced death into the world. Who was keeping them from the tree of life? An angel with a flaming sword. Who else is known as the word of God and has a two-edged sword?
For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.
(Whole Chapter: Hebrews 4 In context: Hebrews 4:11-13)
In his right hand he held seven stars, and out of his mouth came a sharp doubleedged sword. His face was like the sun shining in all its brilliance.
(Whole Chapter: Revelation 1 In context: Revelation 1:15-17)
I ask this question to make this point: That Jesus, the word of God (John 1), will only grant eternal life to those who come to the father through Him.
6 Jesus answered, "I am the way and the truth and the life. No one comes to the Father except through me. (NIV)
Coming to the father through Him entails:
2. Being born again.
After they broke the spiritual wall of God's protection (in breaking the law), and let the devil into their mind, they hid from God.
6 When the woman saw that the fruit of the tree was good for food and pleasing to the eye, and also desirable for gaining wisdom, she took some and ate it. She also gave some to her husband, who was with her, and he ate it. 7 Then the eyes of both of them were opened, and they realized they were naked; so they sewed fig leaves together and made coverings for themselves.
8 Then the man and his wife heard the sound of the LORD God as he was walking in the garden in the cool of the day, and they hid from the LORD God among the trees of the garden. 9 But the LORD God called to the man, "Where are you?"
10 He answered, "I heard you in the garden, and I was afraid because I was naked; so I hid."
11 And he said, "Who told you that you were naked? Have you eaten from the tree that I commanded you not to eat from?"
Their innocence had been corrupted by the knowledge of evil. Before they disobeyed God’s command, there was no evil to have knowledge of. They gained a concept of good and bad. Who did they gain it from? Can it be trusted? Everyone has opinions of what is good and bad for them. God’s opinion is the only correct one.
By believing the devil’s idea to introduce evil, they gave him authority of this world:
the devil took him to a very high mountain and showed him all the kingdoms of
the world and their splendor. 9"All this I will give you,"
he said, "if you will bow down and worship me."
10Jesus said to him, "Away from me, Satan! For it is written: 'Worship the Lord your God, and serve him only.' "
11Then the devil left him, and angels came and attended him.
Since the children have flesh and blood, he too shared in their humanity so that by his death he might destroy him who holds the power of death–that is, the devil–
(Whole Chapter: Hebrews 2 In context: Hebrews 2:13-15)
Satan, not God, is the author of evil.
We are all born into this sin since we are his descendants.
20 Then Noah built an altar to the LORD and, taking some of all the clean animals and clean birds, he sacrificed burnt offerings on it. 21 The LORD smelled the pleasing aroma and said in his heart: "Never again will I curse the ground because of man, even though  every inclination of his heart is evil from childhood. And never again will I destroy all living creatures, as I have done.
We are all also the descendants of Noah, so this scripture establishes the doctrine of original sin in either case.
1Co 15:21 For just as death came by means of a man, in the same way the rising from death comes by means of a man.
1Co 15:22 For just as all people die because of their union with Adam, in the same way all will be raised to life because of their union with Christ.
If you are the best person in the world, then you still must be born again:
Nevertheless, death reigned from the time of Adam to the time of Moses, even over those who did not sin by breaking a command, as did Adam, who was a pattern of the one to come.
(Whole Chapter: Romans 5 In context: Romans 5:13-15)
Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned–
(Whole Chapter: Romans 5 In context: Romans 5:11-13)
1 Peter 1:23
23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever. (KJV)
Jesus has authority over the devil.
how God anointed Jesus of Nazareth with the Holy Spirit and power, and how he went around doing good and healing all who were under the power of the devil, because God was with him.
(Whole Chapter: Acts 10 In context: Acts 10:37-39)
He who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil's work.
(Whole Chapter: 1 John 3 In context: 1 John 3:7-9)
However, He does not use His authority to steal the whole world back from the devil. He vests the authority to trample on the devil’s works in his born-again believers:
He who has an ear, let him hear what the Spirit says to the churches. To him who overcomes, I will give the right to eat from the tree of life, which is in the paradise of God.
(Whole Chapter: Revelation 2 In context: Revelation 2:6-8)
"Blessed are those who wash their robes, that they may have the right to the tree of life and may go through the gates into the city.
(Whole Chapter: Revelation 22 In context: Revelation 22:13-15)
And if anyone takes words away from this book of prophecy, God will take away from him his share in the tree of life and in the holy city, which are described in this book.
(Whole Chapter: Revelation 22 In context: Revelation 22:18-20)
The Holy city is better than