Anyone who takes the time to carefully read and analyze the scriptures will immediately become aware of how many times the bible emphasizes on the sinfulness and weakness of man. In the world of the scriptures there are only two sides: good and evil. There is no grey area either you serve God or you are his enemy. The bible strongly advocates the "either you are with us or against us" attitude.
"For if, while we were God's enemies, we were reconciled to him through the death of his Son, how much more, having been reconciled, shall we be saved through his life!" Romans 5:10
Today's modern day more liberal Christians claim that the story of Adam and Eve and the fall of man was not meant to be taken literally but that it was an allegorical story. I completely disagree with this new interpretation because if this were true what would be the point in stating that Adam lived and died at the age of 930 years old. (Gen. 5:6). Not to mention the fact that the bible also gives Adam a lineage. I am convinced that the author(s) of that tale believed that it was a literal and historical event. Even Paul seemed to believe this tale was based on a literal historical event and not an allegorical fiction.
"For if, while we were God's enemies, we were reconciled to him through the death of his Son, how much more, having been reconciled, shall we be saved through his life!" Romans 5:14
"For as in Adam all die, so in Christ all will be made alive." Romans 5:22
According to the book of Romans all men were cursed because of the sin (disobedience) of Adam. This later led God to destroy mankind because of his sinful nature which the good Lord thought of as deplorable. It made him so angry that he actually said:
5The Lord saw how great the wickedness of the human race had become on the earth, and that every inclination of the thoughts of the human heart was only evil all the time. 6The Lord regretted that he had made human beings on the earth, and his heart was deeply troubled. Genesis 6:5-6
It is because of Adam that we have all inherited the sinful nature that as atheists we now enjoy. The definition of sin is basically any act of disobedience or offense to God. This is why I state often that sin is a nonexistent concept that loses all of its meaning outside the confines of religious belief.
Regarding guilt it also is a constant theme in the scriptures. You are told in the scriptures that it is impossible to live a good life without God. The need for God is emphasized emphatically and you are made to feel inferior without him. Even Jesus promoted this idea when someone asked him a question and called him good. He allegedly replied:
"Why do you call me good?" Jesus answered. "No one is good--except God alone." Mark 10:18
In the eyes of God no one is worthy to approach him. By the standards of the same god no one is good without accepting that they are sinners and in need of redemption. Redemption can only come through Christ and fully believing and trusting in his sacrificial act on mans behalf. In the mind of the Christian there is no other way to redemption. That is why they are so intolerant towards other belief systems. Their bible is the true word of God, and their way is the only way. All others are false beliefs and deceptions of Satan and friends and truth can only be obtained through Christ.
1My dear children, I write this to you so that you will not sin. But if anybody does sin, we have an advocate with the Father—Jesus Christ, the Righteous One. 2He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world. 1 John 2:1-2
As a believer you are reminded that you have to fear the Lord:
"Do not be afraid of those who kill the body but cannot kill the soul. Rather, be afraid of the One who can destroy both soul and body in hell." Matthew 10:28
Note: All scripture quotations are taken from the New International Version.