I believe when man was created in the image of God, we had perfect fellowship with Him. Wanting us to love and obey Him willfully, God gave man a choice and provided guidelines and told him to eat freely of any tree in Eden except for one; the tree of the knowledge of good and evil.
Gen 2:15-17
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."
(from New International Version)
With some help from a certain serpent, Eve chose to eat of this tree anyway as she saw that it was attractive and would certainly be good to taste.
Gen 3:1-5
3:1 Now the serpent was more crafty than any of the wild animals the LORD God had made. He said to the woman, "Did God really say, 'You must not eat from any tree in the garden'?" (notice here that the serpent takes what God said out of context by saying, 'any tree'; he has not changed his strategy a bit!)
2 The woman said to the serpent, "We may eat fruit from the trees in the garden, 3 but God did say, 'You must not eat fruit from the tree that is in the middle of the garden, and you must not touch it, or you will die.'"
4 "You will not surely die," the serpent said to the woman. 5 "For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil."
(from New International Version)
Eve perceived that understanding between good and evil would make her more like God, so pride was ultimately her downfall, and Adam gave in to the same temptation.
Gen 3:6-7
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.
(from New International Version)
I find God's treatment of the situation to be a very interesting view into the character of God:
Gen 3:8-9
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?"
(from New International Version)
As the Bible says that God is omnipresent (existing everywhere) and omniscient (knowing all things), this question seems out of character, but I believe God wasn't trying to ascertain Adam's geographical whereabouts as much as He was trying to help Adam to realize what had occurred when he disobeyed. What He was really asking was, "Adam, where is your heart with me?" so Adam would do some analysis of himself and realize fellowship with his Creator had been broken. God's only concern is our hearts, and He uses every circumstance in life to help us realize where we are with Him; as creatures of His creation made for His enjoyment and glory, this is the most important question that can be asked.
Now the bad news; since Adam fell and sinned against God, and was subsequently cast out of God's fellowship, we, being from the same bloodline, inherited that same propensity to disobey God. I speak of what the Bible describes as the "sinful nature". This is that force within us that causes sin, and must be dealt with above all. The acts of sin that we commit are just a result of this nature working in us, so there are two kinds of sin, the act, and the nature that produces the act.
Rom 5:12
12 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-
(from New International Version)
So the sin
nature was passed to us from Adam, and the result was that we committed the act of sin, in fact, we can do nothing else.
Rom 3:23
23 for all have sinned and fall short of the glory of God,
(from New International Version)
Eccl 7:20
20 There is not a righteous man on earth
who does what is right and never sins.
(from New International Version)
Gal 3:22
22 But the Scripture declares that the whole world is a prisoner of sin,
(from New International Version)
1 John 1:8
8 If we claim to be without sin, we deceive ourselves and the truth is not in us.
(from New International Version)
It would be to your benefit for me to leave you at this point for a time to ponder your fallen state before a righteous and holy God. What comes next is grace, which is never sweeter than when it is given in our hour of most dire need; when we are laid low and understand how unworthy we really are.
But on to the good news. God did not leave it at that, but carefully restored us to fellowship with him by making the ultimate sacrifice. In the Old Testament, in order for sin to be forgiven, the blood (or life) of a spotless animal had to be spilled annually. The animal died as a propitiation, or appeasement, for the sins that were committed, so God's justice was satisfied for all the sinful acts of the prior year and punishment, which sin deserves, was avoided (phew!). These animal sacrifices were not the end, but were a shadow of things to come and in fact only dealt with the act of sin and not the nature that was guilty of committing them.
God desired to make one final sacrifice, which would satisfy His justice once and for all, so that we could be restored to fellowship with Him unconditionally and permanently. What He did was send a perfect man, Jesus Christ, to live on the earth for 33 years without sin (the lamb without blemish or spot):
Isaiah 53:9
9 He was assigned a grave with the wicked,
and with the rich in his death,
though he had done no violence,
nor was any deceit in his mouth.
(from New International Version)
Jesus lived on earth for the purpose of being the ultimate example of a life that was lived to please God. But even He knew that His purpose in coming here was to die, to be a propitiation for all of mankind.
1 John 2:1-2
2 He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
(from New International Version)
2 Cor 5:21
21 God made him who had no sin to be sin for us, so that in him we might become the righteousness of God.
(from New International Version)
Rom 5:6-8
6 You see, at just the right time, when we were still powerless, Christ died for the ungodly. 7 Very rarely will anyone die for a righteous man, though for a good man someone might possibly dare to die. 8
But God demonstrates his own love for us in this: While we were still sinners, Christ died for us.
(from New International Version)
Christ satisfied the Law of God through His death.
So you see, the answer to the big question, "How does one get to heaven?" what I like to call enjoying fellowship with God forever, is really very simple.
Rom 10:9-11
9 That if you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. 10 For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved.
(from New International Version)
Notice I have said nothing about some number of works that you must do; no pilgrimage, no chants, no "Our Fathers". The verse above clearly states, "It is with your heart that you believe and are justified". So it is a matter of belief! Christ did everything, and we must simply lay hold of it! That really is "good news"!
What must one do to avoid heaven? That too is simple. Ignore the facts that were just given to you and you will die separated from God, which is the second, or spiritual, death.
Rom 6:23
23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
(from New International Version)