In tajtaniboo kaba-ira ma tunhawna AAanhu nukaffir AAankum sayyi-atikum wanudkhilkum mudkhalan kareema (surah Nisa: 31)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(4:31) But if you avoid the major sins which you have been forbidden, We shall remit your (trivial) offences, *53 and cause you to enter an honourable abode.

In tajtaniboo kabaaa`ira maa tunhawna `anhu nukaffir `ankum saiyiaatikum wa nudkhilkum mudkhalan kareemaa

*53). God is not overly exacting and severe in His judgements. He is not on the look out for trivial omissions and lapses on the part of His creatures in order to punish them. God is prepared to condone minor omissions, and may even spare a man from being presented with a charge-sheet provided his record is free of major sins. But if a man's record is full of major transgressions, he will be required to explain all the sins he has committed - both major and minor.
We need at this stage to grasp the essential differences between major and minor sins. After reflecting on this question, in the light of the Qur'an and Sunnah, it seems to me - and God alone knows what is absolutely correct - that three elements turn an act into a major sin:
(1) Violation of rights - be it either the rights of God, of parents, of other human beings or even of one's own self. The greater a person's rights, the greater is the sin in violating them. Hence sin is characterized in the Qur'an as wrong-doing (zulm). It is for the same reason that associating others with God in His divinity is called the 'great wrong' in the Qur'an. (See, for example, Surah Luqman 31: 13 - Ed.)
(2) Insufficient fear of God, and arrogance and indifference towards Him, as a result of which man does not heed God's commandments, even wilfully violates them, and deliberately desists from carrying them out. The greater the brazenness, temerity and fearlessness with which one disobeys God, the more heinous is the sin in His eyes. It is for this reason that sin is also termed ma'siyah (disobedience) and fisq. (See, for instance, Surah al-Baqarah 2: 26, 61; Surah al-Hujurat 49: 11; Surah al-Munafiqun 63: 6; Surah Hud 11: 59; Surah AI 'Imran 3: 112; Surah al-Nisa' 4: 42; Surah al-Ma'idah 5: 78; and passim for verbal forms derived from the word ma'siyah and fisq - Ed.)
(3) Sin is aggravated by breaking those bonds and relationships on which the peace and tranquillity of social order rest. These bonds include the relationship between a man and his Lord, as well as that between a man and his fellow-beings. The more important a bond is, the greater is the harm done to the peace of human society when that bond is broken. Likewise, the stronger the expectation that the sanctity of a certain bond will be honoured, the greater is the sin incurred through its desecration. Let us take the case of unlawful sexual intercourse in its various degrees. This act is inimical to the existence of a sound social order and is therefore a major sin. But in certain cases the sin becomes even graver. For instance, it is more serious if committed by a married person than by one who is unmarried. Similarly, unlawful sexual intercourse with a married woman is graver than with an unmarried woman. Again, to commit this act with one's neighbours is more heinous than with others, and to commit this act with women within the prohibited degrees, such as one's sister, daughter or mother, is far more abominable than with others. Further still, it is a much graver sin to commit such an act in places of worship than elsewhere. The difference in the degree of such sinfulness is based on the considerations we have mentioned above. Wherever the sanctity "of a relationship is normally respected, wherever there is a bond which deserves to be held sacred, and wherever the disruption of a particular relationship is likely to result in greater harm and corruption, the gravity of the sin increases. This is why in certain places the Qur'an uses the term fujur to denote sin. (See, for instance, Surah al-Qiyamah 75: 5; Surah al-Infitar 82: 14; Surah al-Shams 9l: 8 - Ed.)