The Bible: In the Bible, all sin is against God. The Scriptures compare the Old Testament relationship between God and Israel with marriage, and Israel's rebellion against Him with adultery. The Lord is angry over human sin, but at the same time grieved. "But they rebelled and grieved His Holy Spirit (Isaiah 63:10. Compare Eph. 4:30). In his well-known prayer of repentance (Psalm 51), David recognises, "Against You, You only have I sinned." (vs. 6. Compare 1 Kings 8:50).
The Koran: In the whole Koran text there is no mention of original sin. Rather, the book teaches that every human being can choose between Good and Evil in every action. According to Islam, God permits the Satan to tempt men to disobedience, so that Evil does not come out of man's inner being-which is what Scripture teaches-but from external temptation, from the whispering of the Devil. If one resists and does not wish to do Evil, then he is able to achieve Good.
As we see here, the Koran has a thouroughly positive view of Man in terms of his moral capabilities. He is not unable to do the Good, as the Bible describes the unredeemed, but suffers from weaknesses which originate in his unbelief. Tilmann Nagel concludes, "The Koran's view of human nature, which seems to be marked by weaknesses of character, is still completely optimistic and positive, for these weaknesses are considered to be the fruits of unbelief."
The Bible: The main idea of Romans 7:19, "For the good that I will to do, I do not do; but the evil I will not to do, that I practice." is not to be found in Islam, for man is believed to be able to achieve the Good. Just as in the Bible, the Koran describes sin as transgression against God's law and disobedience of all His commands, but not as the rebellion of the inner man against God Himself and His Law. Jesus, describing the origin of Evil, says, "For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man." (Mark 7:21-23)
The Koran: Man is basically able to not sin. If he listens to Evil and does wrong, God is merciful and willing to forgive offences, as long as the individual is sorry and wishes to improve. If he performs his prayers regularly, observes the month of fasting, gives alms and perhaps carries out the pilgramage to Mecca, he may hope that Allah will graciously permit him to enter Paradise when he dies.
On the other hand, Man has the possibility of choosing to do Evil. The Koran speaks clearly of those who do not listen to God's warnings, but never leaves the impression that all men would ever be prepared to obey the teachings of His messenger. This becomes clear in the so-called "Legends of Punishment", which describe the destruction of whole nations who ignored God's warnings, even though they should have believed the Prophet. In the same way, Mohammed addresses his warnings of the coming judgement to his contemporaries, and must still experience their rejection of his message.
The Bible: Man is essentially incapable of not sinning, for he is "sold under sin" (Rom. 7:14-15). He is under its curse and continues to commit Evil until he accepts God's forgiveness. Only by accepting the fact that he is a sinner, that he cannot improve himself, and that Jesus died on the Cross because of his sin, can he be reconciled with God and receive new life through repentance and prayer. Only then, does the Holy Spirit dwell in him and enable him to resist sin through the power of God. Should he then sin-which will occur repeatedly in the life of the Christian-but ask for forgiveness for his transgression, he will receive forgiveness and new fellowship with his Creator (1 John 1:9). Whoever becomes a child of God in this way, has the confidence that he will inherit eternal life.
1. Unbelief (Arabic-'kufr'): Unbelief is the greatest sin of all. It can be expressed
a. in the denial of the existence and the activity of God.Whoever commits these sins and fails to repent before death, cannot, according to probably all Moslem theologians, enter Paradise. Such a person will be cast by God into the fires of Hell for all eternity.
b. in the repudiation of Islam
c. in the worship of gods other than Allah. For this reason, Jews and Christians are considered to be guilty of polytheism; the Jews, because they are believed to worship Esra as the son of God (Surat 9:30), the Christians, because they have declared Jesus to be divine (Surat 5:72).
2. Greater (or graver) sins: This includes offences such as the rebellion and disobedience of children against their parents, murder, perjury, doubting God's forgiveness, incessant sin, calculation of God's grace, false testimony, magic, slander about indecency, drinking alcohol, misuse of the orphan's possessions, usury, adultery, homosexuality, theft and desertion from the army.
All grave sins, including murder and adultery, can be forgiven to a pious Moslem, for he can expect the mediation of the Prophet Mohammed at the Last Judgement.
3. Lesser (or lighter) sins: The Koran mentions not only "greater sins and indecencies"(Surat 42:37), but also lighter offences. (Surat 53:32). Little sins, popular Islam assumes, can be expiated by good deeds such as giving alms, additional fasting or prayers. God would never refuse Paradise to a Moslem who had committed only lesser offences.
As a result of this differentiation between greater and lesser sins, the question arises, whether a Moslem who commits grave sins can still be considered a believer or if he has proven himself to be a renegade damned to the punishments of Hell.
Here again, the opinions of Moslem theologians vary on this point. Some assume that a Moslem can lose his salvation by commiting grave sin. The Harijites, for example, teach that one who commits serious transgressions must be an unbeliever (Arabic-'kâfir'). The Wa'idites, a splinter group of the Hârijites, also doubted whether such a sinner could still be counted as a believer. The Zaidites, a sub-group of the Shiites and the Ibâdites (another sub-group of the Hârijites) assumed that such a great sinner would remain in the fire eternally.
The Mu'tazilites, however, taught that Moslems who commit grave sins constitute a third class between the believers and the unbelievers, the class of the wicked (Arabic-'al-fâsiqûn'), those who confess Islam but have become bound in serious sin. If he ceases to transgress, he then becomes a believer again. Should the wicked man die before repenting, he will be considered by God to be an unbeliever.
The opinions above do not, however, represent the views of the majority of Moslem theologians. Most assume that each Moslem will enter Paradise, even if he has committed serious sins, but could not repent of them before death. God will perhaps condemn him to a period of time in Hell, but then, because of Mohammed's mediation, receive him into Paradise for eternity. (This corresponds to the Catholic dogma of Purgatory.) Should the unbeliever ask for forgiveness before his death, then God is sure to forgive him and receive him into Paradise without prior punishment.
 Tilmann Nagel. Der Koran. Einführung-Texte-Erläuterungen, Verlag C. H. Beck, (Munich, l983), p. 253.
 Hermann Stieglecker. Die Glaubenslehren des Islam, Ferdinand Schöningh, (Paderborn, l963), pp. 625-626.
 E. E. Elder. "The Development of the Muslim Doctrine of Sins and their Forgiveness", The Moslem World, 29/l939, pp. 178-183. See also Stieglecker, Ibid., p. 634.