1. Introduction: 3
2. Defination of sin 3
3. Origin of sin 3
4. The doctrine of inherited sin 4
1. Inherited guilt 4
2. Inherited corruption 6
I take Christian Education class for the church members. One day a young person asked “ It is unfair we are counted guilty because of Adam’s sin as Rom 5:12-21 teaches.
I made a study and took a session to answer him so that his sense of unfairness will not become a hindrance in his relationship with God. I give here the details of the study on sin.
The Definition of Sin
The history of the human race as presented in Scripture is primarily a history of man in a state of sin and rebellion against God and of God’s plan of redemption to bring man back to himself. Therefore, it is appropriate now to consider the nature of the sin that separates man from God.
We may define sin as follows: Sin is any failure to conform to the moral law of God in act, attitude, or nature. Sin includes not only individual acts such as stealing or lying or committing murder, but also attitudes that are contrary to the attitudes God requires of us.
Here God specifies that a desire to steal or to commit adultery is also sin in his sight. The Sermon on the Mount also prohibits sinful attitudes such as anger (Matt. 5:22) or lust (Matt. 5:28). Paul lists attitudes such as jealousy, anger, and selfishness (Gal. 5:20) as things that are works of the flesh opposed to the desires of the Spirit (Gal. 5:20). Therefore a life that is pleasing to God is one that has moral purity not only in its actions, but also in its desires of heart. In fact, the greatest commandment of all requires that our heart be filled with an attitude of love for God: “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength” (Mark 12:30). 
The Origin of Sin
Where did sin come from? How did it come into the universe? First, we must clearly affirm that God himself did not sin, and God is not to be blamed for sin. It was man who sinned, and it was angels who sinned, and in both cases they did so by wilful, voluntary choice.
Even before the disobedience of Adam and Eve, sin was present in the angelic world with the fall of Satan and demons. But with respect to the human race, the first sin was that of Adam and Eve in the Garden of Eden (Gen. 3:1–19). Their eating of the fruit of the tree of the knowledge of good and evil is in many ways typical of sin generally.
First, their sin struck at the basis for knowledge, for it gave a different answer to the question, “What is true?” Whereas God had said that Adam and Eve would die if they ate from the tree (Gen. 2:17), the serpent said, “You will not die” (Gen. 3:4). Eve decided to doubt the veracity of God’s word and conduct an experiment to see whether God spoke truthfully.
Second, their sin struck at the basis for moral standards, for it gave a different answer to the question “What is right?” God had said that it was morally right for Adam and Eve not to eat from the fruit of that one tree (Gen. 2:17). But the serpent suggested that it would be right to eat of the fruit, and that in eating it Adam and Eve would become “like God” (Gen. 3:5). Eve trusted her own evaluation of what was right and what would be good for her, rather than allowing God’s words to define right and wrong. She “saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was to be desired to make one wise,” and therefore she “took of its fruit and ate” (Gen. 3:6).
Third, their sin gave a different answer to the question, “Who am I?” The correct answer was that Adam and Eve were creatures of God, dependent on him and always to be subordinate to him as their Creator and Lord. But Eve, and then Adam, succumbed to the temptation to “be like God” (Gen. 3:5), thus attempting to put themselves in the place of God.
The Doctrine of Inherited Sin
How does the sin of Adam affect us? Scripture teaches that we inherit sin from Adam in two ways.
1. Inherited Guilt: We Are Counted Guilty Because of Adam’s Sin. Paul explains the effects of Adam’s sin in the following way: “Therefore...sin came into the world through one man and death through sin, and so death spread to all men because all men sinned” (Rom. 5:12).
When Adam sinned, God thought of all who would descend from Adam as sinners. Though we did not yet exist, God, looking into the future and knowing that we would exist, began thinking of us as those who were guilty like Adam. This is also consistent with Paul’s statement that “while we were yet sinners Christ died for us” (Rom. 5:8). Of course, some of us did not even exist when Christ died. But God nevertheless regarded us as sinners in need of salvation. The conclusion to be drawn from these verses is that all members of the human race were represented by Adam in the time of testing in the Garden of Eden. As our representative, Adam sinned, and God counted us guilty as well as Adam.
When we first confront the idea that we have been counted guilty because of Adam’s sin, our tendency is to protest because it seems unfair. We did not actually decide to sin, did we? Then how can we be counted guilty? Is it just for God to act this way?
In response, three things may be said:
(1) Everyone who protests that this is unfair has also voluntarily committed many actual sins for which God also holds us guilty. These will constitute the primary basis of our judgment on the last day, for God “will render to every man according to his works” (Rom. 2:6), and “the wrongdoer will be paid back for the wrong he has done” (Col. 3:25).
(2) Moreover, some have argued, “If any one of us were in Adam’s place, we also would have sinned as he did, and our subsequent rebellion against God demonstrates that.”
(3) The most persuasive answer to the objection is to point out that if we think it is unfair for us to be represented by Adam, then we should also think it is unfair for us to be represented by Christ and to have his righteousness imputed to us by God. For the procedure that God used was just the same, and that is exactly Paul’s point in Romans 5:12–21: “As by one man’s disobedience many were made sinners, so by one man’s obedience many will be made righteous” (Rom. 5:19). Adam, our first representative sinned—and God counted us guilty. But Christ, the representative of all who believe in him, obeyed God perfectly—and God counted us righteous. That is simply the way in which God set up the human race to work. God regards the human race as an organic whole, a unity, represented by Adam as its head. And God also thinks of the new race of Christians, those who are redeemed by Christ, as an organic whole, a unity represented by Christ as head of his people.
2. Inherited Corruption: We Have a Sinful Nature Because of Adam’s Sin. In addition to the legal guilt that God imputes to us because of Adam’s sin, we also inherit a sinful nature because of Adam’s sin. This inherited tendency to sin does not mean that human beings are all as bad as they could be. The constraints of civil law, the expectations of family and society, and the conviction of human conscience (Rom. 2:14–15) all provide restraining influences on the sinful tendencies in our hearts. Therefore, by God’s “common grace” people have been able to do much good in the areas of education, the development of civilization, scientific and technological progress, the development of beauty and skill in the arts, the development of just laws, and general acts of human benevolence and kindness to others. In fact, the more Christian influence there is in a society in general, the more clearly the influence of “common grace” will be seen in the lives of unbelievers as well. But in spite of the ability to do good in many senses of that word, our inherited corruption, our tendency to sin, which we received from Adam, means that as far as God is concerned we are not able to do anything that pleases him.
This may be seen in two ways:
In Our Natures We Totally Lack Spiritual Good Before God: It is not just that some parts of us are sinful and others are pure. Rather, every part of our being is affected by sin—our intellects, our emotions and desires, our hearts (the center of our desires and decision-making processes), our goals and motives, and even our physical bodies. Paul says, “I know that nothing good dwells within me, that is, in my flesh” (Rom. 7:18), and, “to the corrupt and unbelieving nothing is pure; their very minds and consciences are corrupted” (Titus 1:15). Moreover, Jeremiah tells us that “the heart is deceitful above all things, and desperately corrupt; who can understand it?” (Jer. 17:9). In these passages Scripture is not denying that unbelievers can do good in human society in some senses. But it is denying that they can do any spiritual good or be good in terms of a relationship with God. Apart from the work of Christ in our lives, we are like all other unbelievers who are “darkened in their understanding, alienated from the life of God because of the ignorance that is in them, due to their hardness of heart” (Eph. 4:18).
In Our Actions We Are Totally Unable to Do Spiritual Good Before God: This idea is related to the previous one. Not only do we as sinners lack any spiritual good in ourselves, but we also lack the ability to do anything that will in itself please God and the ability to come to God in our own strength. Paul says that “those who are in the flesh cannot please God” (Rom. 8:8). Moreover, in terms of bearing fruit for God’s kingdom and doing what pleases him, Jesus says, “Apart from me you can do nothing” (John 15:5). In fact, unbelievers are not pleasing to God, if for no other reason, simply because their actions do not proceed from faith in God or from love to him, and “without faith it is impossible to please him” (Heb. 11:6). When Paul’s readers were unbelievers, he tells them, “You were dead through the trespasses and sins in which you once walked” (Eph. 2:1–2). Unbelievers are in a state of bondage or enslavement to sin, because “every one who commits sin is a slave to sin” (John8:34). Though from a human standpoint people might be able to do much good, Isaiah affirms that “all our righteous deeds are like a polluted garment” (Isa. 64:6; cf. Rom. 3:9–20). Unbelievers are not even able to understand the things of God correctly, for the “natural man does not receive the gifts [lit. “things’] of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned” (1 Cor. 2:14 RSV mg.). Nor can we come to God in our own power, for Jesus says, “No one can come to me unless the Father who sent me draws him” (John 6:44).
But if we have a total inability to do any spiritual good in God’s sight, then do we still have any freedom of choice? Certainly, those who are outside of Christ do still make voluntary choices—that is, they decide what they want to do, then they do it. In this sense there is still a kind of “freedom” in the choices that people make.14 Yet because of their inability to do good and to escape from their fundamental rebellion against God and their fundamental preference for sin, unbelievers do not have freedom in the most important sense of freedom—that is, the freedom to do right, and to do what is pleasing to God.
The application to our lives is quite evident: if God gives anyone a desire to repent and trust in Christ, he or she should not delay and should not harden his or her heart (cf. Heb. 3:7–8; 12:17). This ability to repent and desire to trust in God is not naturally ours but is given by the prompting of the Holy Spirit, and it will not last forever. “Today, when you hear his voice, do not harden your hearts” (Heb. 3:15).
Without the supernatural regeneration by the Holy Spirit, all men would remain in their fallen state. But in His grace, mercy and loving-kindness, God sent His Son to die on the cross and take the penalty of our sin, reconciling us to God and making eternal life with Him possible. What was lost at the Fall is reclaimed at the Cross.
Grudem, Wayne, Systematic Theology, GS books Hyderabad 2015
http://www.gotquestions.org/fall-affect-humanity.html accessed on 14 Sept 2016
 Wayne Grudem, Systematic Theology ( GS books Hyderabad 2015 ) 490
 Wayne Grudem, Systematic Theology ( GS books Hyderabad 2015 ) 492
 Wayne Grudem, Systematic Theology ( GS books Hyderabad 2015 ) 494
 http://www.gotquestions.org/fall-affect-humanity.html accessed on 14 Sept 2016