Belief in Resurrection Day and the Hereafter are one of the most important and significant pillars of faith and Islamic Principles; they are among the main conditions of being a Muslim. In more than a hundred verses, the Holy Qur'an has spoken about the characteristics of eternal life, and in sixteen verses has officially mentioned that a firm belief in the afterlife is followed inevitably, by having faith in God; in a few cases, it has even included that Certitude [i.e. Certainty-Conviction] in the Afterlife is among the characteristics of true believers.1
Indeed, the Holy Qur'an has spoken about the Resurrection Day, with various interpretations and exegesis; and each one of these interpretations is a separate portal for acquiring a better knowledge of it; one such example is the word “Al-Yaom Al- Akhir” [i.e. Judgment Day - Resurrection Day], which mentions two things:
1. The Human life is divided into two main "periods"; and each one is interpreted as one “Day” per se. The first Period [i.e. the life on Earth] is finite and ephemeral, whereas the second period [i.e. the afterlife] is infinite and eternal.
2. Our spiritual happiness and beatitude in either worlds [or Periods] depends on our faith in the afterlife.
To begin with, our happiness in this world of ours depends on our faith in the Resurrection Day.
This is because in the light of having faith in the eternal life, we come to be aware of the quality of immortality and eternity in our deeds; and of our Judgment by the Powerful Creator; and then of our responsibility towards all these notions and concepts. Therefore, eventually, we attempt to purify, to better our intentions and deeds, and to prevent ourselves from committing all kinds of perversities and wrongdoings. Consequently, to believe in Resurrection Day guides us towards goodness and it appears as a support for all the human values that we cherish most; it also prevents the human being from all kinds of sins, misdeeds, and wickedness. It then makes him understand that without having this deep belief, his life will be tormented by all kinds of darkness, abominations, impurities, and stains…
Secondly, to believe in Resurrection Day saves the human being from absurdity and being absurd at the same time. Similarly, being unfamiliar with the hereafter and eternal life provokes undoubtedly a sentiment of meaninglessness, nonsense and absurdity, so that after a while, the individual, burdened by such feelings of fatuousness and restlessness becomes as such, with lots of empty, foolish ideas in his mind.
On the contrary, belief in Resurrection Day allows man to let go of absurdity and unreasonableness2.
Thirdly, our happiness and beatitude in the hereafter depend mostly on our belief in the world beyond and in resurrection, because eternal felicity and eternal torment are related to the deeds and misdeeds of each individual in this earthly plane. And the fact that one is endowed with belief and knowledge in choosing the righteous path, in order to attain happiness and beatitude, while at the same time, one is trying one's best to avoid entering the way of perdition and loss. This is a very crucial and important factor for man to remember.
Indeed, the reality of Resurrection Day is the return to God and the ultimate thing that one has to accomplish. However, according to the Holy Qur'an’s point of view, this particular return is not exclusive and restricted to human beings. It also includes all forms of existence in this wide Universe; then again, in regards to the human beings, one should point out that it shall neither be in an absolutely physical form nor in an absolutely spiritual [i.e. ethereal] form; but in all the possible dimensions, which encompass his "human" being.