Q 5: Is it a pre-condition to avoid grievous sins in order to deserve the promise of forgiveness?
A: Yes, this is a unanimously agreed upon rule according to Ahl-ul-Sunnah wal-Jama'ah (those adhering to the Sunnah and the Muslim main body) that the Promise of Allah (Glorified be He) or the Messenger (peace be upon him) with forgiveness, Paradise or salvation from the Fire is conditional upon avoiding the major sins. Allah (Exalted be He) says: If you avoid the great sins which you are forbidden to do, We shall expiate from you your (small) sins, and admit you to a Noble Entrance (i.e. Paradise). Allah (He may be Praised) explains that one of the conditions of admitting people to Paradise and erasing their sins is to avoid the grievous sins. Allah (Exalted be He) says: If you avoid the great sins which you are forbidden to do, We shall expiate from you your (small) sins, and admit you to a Noble Entrance (i.e. Paradise). This indicates that whoever does not avoid them will not have this outcome because the statement: If you avoid is a condition and its consequent result is: We shall expiate from you your (small) sins This is a rule that the outcome is dependent on fulfilling the condition. Once the condition is fulfilled, the outcome and reward will follow; otherwise they will not occur. So a believer must keep away and avoid the grievous sins.
The major sins refers to the grievous sins that Allah curses, afflicts His wrath upon, or promises to consign their doers to Hellfire. These sins also include the crimes whose commitment imposes Had (ordained punishment for violating Allah's Law) in this world such as Zina (premarital sexual intercourse and/or adultery), robbery, filial disobedience,
cutting the ties of kinship, Riba (usury/interest), usurping the property of orphans, Ghibah (backbiting), Namimah (tale-bearing), cursing, insulting, and other major sins. It is obligatory to greatly beware of them and repent of the previous grave sins committed. It is reported in the Sahih (authentic) Hadith that the Prophet (peace be upon him) said: "The Five (Obligatory Daily) Prayers, and from (one) Friday Prayer to (the next) Friday Prayer, and from Ramadan to Ramadan, are expiations for whatever (sins committed) between them, provided that major sins are not committed." According to another narration: "...provided that major sins are avoided." (Related by Muslim in his Sahih [Authentic Hadith Book])So, it indicates that the great acts of 'Ibadah (worship) erase sins on condition that the grievous sins are avoided. This Hadith is in conformity with the previous Ayah. One time when the Prophet (peace be upon him) was performing Wudu' (ablution), he mentioned that whoever performs Wudu' perfectly, his previous sins shall be forgiven as long as one avoids Al-Maqtalah (i.e. grievous sins). So, a believer must strive to do good, compete in righteous acts, and avoid sins, especially, the grievous ones because their danger is great unless Allah forgives them as long as they are not one of the acts of Shirk (associating others with Allah in His Divinity or worship). Allah (Exalted be He) says: Verily, Allâh forgives not that partners should be set up with Him (in worship), but He forgives except that (anything else) to whom He wills