b) Forgiving Sins through Avoiding Forbidden Things, especially Grave Sins:
A number of forbidden things are clearly stated in the Holy Qur'an and the Sunna of the Prophet (peace be upon him). For example, meat of an animal that is found dead before being
slaughtered, meat of an animal not slaughtered in accordance with ritual requirements (on which the name of other than Allah has been invoked), meat of swine and blood are forbidden; and those who avoid them are promised forgiveness. After a number of forbidden things has been mentioned in the Fifth Chapter of the Qur'an (Surat Al-Ma'ida), warning is given to those who do not yield to Allah's orders:
"If anyone rejects faith, fruitless is his work, and in the Hereafter he will be in the ranks of those who have lost (all spiritual good)."The word faith here has special meaning which encompasses acts of worship such as lawful food, cleanliness, social intercourse, marriage and other interests in life which are linked with our duty to Allah and faith in Him.
As for the Muslim, who resists his own sensuous desires and lusts, and his own inclination towards worldly pleasures which often lead to committing sins, great rewards and forgiveness are awaiting him. Allah says in the Holy Qur'an, "Allah doeth wish to make clear to you and to guide you into the ways of those before you: and (He doeth wish to) turn to you (in Mercy): and Allah is All-knowing, All-wise Allah doeth wish to turn to you, but the wish of those who follow their lusts is that ye should turn away (from Him), Far, far away." And "If ye (but) eschew the most heinous of all things which ye are forbidden to do,
We shall remit your evil deeds, and admit you to a Gate of great honor. "
The most heinous of all things (grave sins) are determined and defined in number of the Prophet's sayings.
Imam Ibn Kathir compiled the sayings of the Companions of the Prophet Mohammed concerning the great destructive sins. He then defined a great destructive sin as the sin whose punishment is Hell in the Hereafter, and which deserves legal punishment in worldly life. Hence, a great destructive sin is one which is clearly forbidden by a statement in the Holy Qur'an or in the Sunna of the Prophet (peace be upon him).
And there is no doubt that atheism and polytheism are the most destructive of all sins. These cannot be remitted or forgiven. Allah says in the Holy Qur'an, "Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth."Explaining why this verse was revealed to the Prophet Mohammed (peace be upon him), Imam Al-Alusi said: When Allah's words, "O my servants who have transgressed against their souls! Despair not of the Mercy of Allah: for Allah forgives all sins"were revealed to the Prophet Mohammed (peace be upon him), he went out to recite them before his
followers. One of them stood up and asked, "What about those who set up partners with Allah?" Allah's Messenger (peace be upon him) gave him no answer. The man repeated his question, and the Prophet Mohammed still kept silent. Then the verse beginning with "Allah forgiveth not that partners....." was revealed to exclude atheists and polytheists from those whose sins can be forgiven. However, the majority of Muslim scholars say that forgiveness may extend to all sins (with no exception) if repentance occurs. Yet, joining others in worship with Allah is a great sin. Abdullah bin Mas'ud narrated: When the following verse was revealed: "It is those who believe (in the Oneness of Allah and worship none but Him Alone) and confuse not their belief with Zulm (wrong .i.e. by worshipping others beside Allah.)", the companions of Allah's Messenger (peace be upon him) asked, "Who is amongst us who had not done Zulm?" Then Allah revealed: "Verily, joining others in worship with Allah is indeed a great Zulm."