Major sins are defined as what is forbidden by Allah and His Messenger in the Qur’an and the Sunnah in addition to what is narrated on the authority of early Muslims. Allah, the Most high, promises whoever avoids the major sins to expiate his minor sins. Allah, the Almighty says,
“If ye (but) eschew the most heinous of the things which ye are forbidden to do, we shall remit your evil
deeds, and admit you to a gate of great honour.” (An-Nisaa :31)
In this text, Allah, the Most High, also promises whoever avoids the major sins to admit him to Paradise.
Allah, the Almighty says,
“Those who avoid the greater sins and indecencies, and when they are angry even they forgive;” (Ash-Shura:37)
The Qur’an also states,
“Those who avoid great sins and indecent deeds, save lesser offences, verily thy Lord is ample in forgiveness.” (An-Najm:32)
The Prophet (pbuh) said,
“The five prescribed Prayers, and from one Friday Prayer to another and from Ramadan to another entail forgiveness for what is between them as long as you do not commit the major sins.” (Muslim, Tirmidhi, Ibn Khuzaymah and Ahmed.)
We are obliged to learn about what the major sins are, so that Muslims may avoid them. Scholars of Sacred knowledge are of different opinions about the number of the major sins. It is argued that they are only seven owing to the Prophet’s (pbuh) saying,
“Avoid the seven heinous sins: Worshipping others with Allah, sorcery, taking a life which Allah has made sacred except in the course of justice, devouring usury, appropriating the property of the orphan, fleeing from the battlefield, and charging believing women, unmindful though innocent, with adultery.” (Bukhari and Muslim.)
Ibn Abbas holds that they are likely counted as seventy not seven. That is a good point of view because enumeration is not intended in the Hadith.
As a matter of fact, any sin entailing either a threat of punishment in the Hereafter explicitly mentioned by the Qur’an or Hadith, a prescribed legal penalty (Hadd), or being accursed by Allah or His Messenger (pbuh) is called a major sin. We have to bear in mind that some major sins are most heinous than another. This is because the Prophet (pbuh) has enlisted Shirk (worshipping others with Allah) though a polytheist will suffer eternal torture in Fire and will never be forgiven.
Allah, the Almighty, says,
“Allah forgiveth not (the sin of) joining other gods with Him, but He forgiveth whom He pleaseth other sins than .” (An-Nisa:116)