There is a special emphasis on the Last Day and its importance in the Book of Allah, may He be Glorified and Exalted, and in the Sunnah of His Prophet (blessings and peace of Allah be upon him). That includes the following:

3.1. Allah has connected belief in Him to belief in the Last Day
Allah, may He be Glorified and Exalted, says (interpretation of the meaning), "What harm would it do them to believe in Allah and in the Last Day, and to spend out of what Allah has bestowed upon them? For Allah has full knowledge of them." (al-Nisa’ 4:39) Allah, may He be Glorified and Exalted, connected belief in Him to belief in the Last Day, and has made it come next in importance to belief in Him. The Prophet (blessings and peace of Allah be upon him) did the same.

It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) said, “Whoever believes in Allah and the Last Day, let him speak good or else remain silent; whoever believes in Allah and the Last Day, let him honour his neighbour; whoever believes in Allah and the Last Day, let him honour his guest.” (Al-Bukhari, Muslim)

So no one can truly believe – even if he says that he believes in Allah – unless he believes in the Last Day. The one who separates the two has no share of faith, even if he claims to. Many of the disbelievers believe in Allah, but they deny the Last Day, so that belief will not benefit them and Allah has permitted the believers to fight them and seize their wealth.

3.2. It is often mentioned in the Holy Qur’an and the Prophetic Sunnah
Hardly any surah in the Holy Qur’an is without mention of the Last Day, which is presented in such a way as to enable people to understand this concept, using different styles, to establish proof and evidence, or to give likenesses. For example, reference is made to the initial creation, the creation of the heavens and the earth, and the revival of dead land to explain the resurrection.

3.3. Many names are used to refer to the Last Day in the Holy Qur’an
There are many names mentioned in the Qur’an which refer to the Last Day, all of which highlight what will happen on that Day of terrors. These names include: the Day of Resurrection, the Day of Reckoning, the Imminent Day, the Day of Judgement, the Day of Great Loss. There are several reasons why the Qur’an pays such great attention to the Last Day, including the following:

i. The polytheists vehemently denied the Last Day, and they attributed what they saw of life and death to time or the passage of time (al-dahr). Allah, may He be Glorified and Exalted, says (interpretation of the meaning), "And they say: There is nothing beyond our life in this world; we die and we live, and nothing but the passage of time causes us to die. They have no knowledge of that; they are merely speculating." (al-Jathiyah 43:24) The Qur’an came down with strong arguments to confront those who denied the Last Day, and it uses various methods to convince the disbelievers that that Day will inevitably come.

ii. The belief of the People of the Book in the Last Day is distorted
They also believe in the Last Day in principle, but their concept of it is distorted and is incorrect. Moreover, Islam brought facts and details about the Last Day that were not known to the followers of previous religions.

iii. The Qur’an affirms that there will be a Day on which the doer of good will be rewarded for his good deeds and the doer of evil will be requited for his evil deeds

Allah has ordained the Last Day so that He may reward the doer of good for his good deeds and requite the doer of evil for his evil deeds, otherwise there would be no difference between doing good deeds and doing bad deeds in this world, and there would be no righteous deeds and no vile deeds, as a result of which life would be chaotic and would lead to an unknown fate.

Allah, may He be Glorified and Exalted, says (interpretation of the meaning), "Does man think that he will be left unchecked?" (al-Qiyamah 75:36) "Did you think that We created you without purpose, and that you would not be brought back to Us?" (al-Mu’minun 23:115) "To Allah belongs all that is in the heavens and all that is on earth, and so He will requite those who do evil for their deeds, and He will reward those who do good with the best reward." (al-Najm 53:31)