Like most religions, Islam teaches that there is another life which begins at the very moment of death. This next life begins with the disconnection of the soul from the body and then progresses through various stages which are known as; Death, the Grave, the Resurrection, the Day of Judgement, and either Paradise or Hellfire.
Belief in the next life and more specifically, the Day of Judgement, is one of the six pillars of faith for Muslims and as such is always at the forefront of the thought process of a Muslim before doing any action. This is because Islam teaches that we will be held accountable for each and every action carried out in this world resulting in either punishment or reward as mentioned in the Qur'an:
“That Day, the people will depart separated [into categories] to be shown [the result of] their deeds. So whoever does an atom's weight of good will see it, And whoever does an atom's weight of evil will see it.” [The Qur'an Al-Zalzalah 99:6-8]
Muslims believe in a life after death and that with the death of an individual, the door into the next life is opened. Allah (God) says in the Qur’an:
“And fear a Day when you will be returned to Allah. Then every soul will be compensated for what it earned, and they will not be treated unjustly.” [The Quran: Al-Baqarah 2:281]
“Every soul will taste death, and you will only be given your [full] compensation on the Day of Resurrection. So he who is drawn away from the Fire and admitted to Paradise has attained [his desire]. And what is the life of this world except the enjoyment of delusion.”
As most people know, death is the only certainty in life, and no matter who you are or where you are, death will eventually come to you. This is clearly mentioned in the Qur’an:
“Wheresoever you may be, death will overtake you even if you are in fortresses built up strong and high!”
Belief in life after death is one of the Six Pillars of Faith in Islam, and it is a prerequisite to believe in this to become a muslim, as it is mentioned in the Quran:
“O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah , His angels, His books, His messengers, and the Last Day he has certainly gone far astray” [The Quran: An-Nisaa’ 4:136]
Also, this is mentioned in the sayings of the Prophet Muhammad (May the Peace and Blessings of Allah be upon him), who said regarding the resurrection:
“..[and] Allah will send water from the sky and the the dead bodies will grow like vegetation grows, ..” [Bukhari: 4935]
Belief in the after-life is very important to Muslims, and just as they firmly believe in it because of the fact that they were told about it by Allah, believing in it also helps improve their actions and behaviour in this life. It gives the lowly and the oppressed a hope and an anticipation for a higher justice that none will escape from, and it causes people to become god-fearing as they know that one day God will judge between people regarding their belief and their actions.
It is a constant reminder for Muslims to think about every action that they do, and whether they will be questioned about it on the Day of Judgement or not. A perfect example of this is in the statement of ‘Umar ibn Abd Al-’Aziz, who was one of the rulers of the Islamic empire and the great grandson of one of the most senior disciples of the Prophet Muhammad [May the Peace and Blessings of Allah be upon him]). It is mentioned that once when a man verbally abused him, he remarked: “If it wasn’t for the Day of Judgement I would have replied to you.”
Belief in the afterlife is not only unique to Muslims, other religions also have a concept of a life after death, although they differ over the exact nature. For example, Jews believe in a life after death which includes a physical resurrection of the dead, even though some in the same religion believe in reincarnation. Christians, like Muslims, believe in the Day of Judgement and Paradise and Hellfire, but differ regarding the specifics of each stage. On the other hand, Buddhists and Hindus do not believe in a physical resurrection, but only in a spiritual rebirth of the soul.
In conclusion, belief in a life after death is a fundamental aspect of the Islamic belief and always takes center place in the mind of a Muslim, in the sense that, each and every action is thought about prior to it's undertaking, in regards to whether it will be of benefit or detriment in the life to come.