How can the Divine Universal Mercy be reconciled with instances of death and decay?

In the Name of God, the Merciful, the Compassionate.

We have made all that is on earth an ornament thereof that we may test them: which of them is best in conduct. Verily, We shall make all that is thereon a barren mound. (18:7-8)

Naught is the light of the world save a pastime, a sport. (6:32)

God has made this world in the form of a festival

The All-Compassionate Creator, the All-Munificent Provider, the All-Wise Maker, has made this world in the form of a festival, a place of celebration for the world of spirits and spirit beings, and decorated it with most wonderful inscriptions of His Names. Clothing each spirit, great or small, exalted or lowly, in a corporeal form, a body equipped with senses suitable to it and appropriate for it to benefit from the innumerable, various good things and bounties in the festival. He sends each to this spectacle once. He divides the festival, which is very extensive in regard to both time and space, into centuries, years, seasons and days, and into certain parts, and makes each an exalted festival during which all groups of His animal creatures and plants promenade. Especially in spring and summer, the surface of the earth constitutes a vast arena of festivals one after another for the multitudes of small creatures, an arena so glittering and attractive that it draws the gaze of angels and other inhabitants of the heavens, and spirit beings in the higher abodes. Also, for the people who think and reflect, it is an arena for reflection so wonderful that the mind is unable to describe it.

However, the manifestations of the Divine Names, the Most Merciful and Giver of Life, in this Divine feast and festival, are counterbalanced by the Names, the All-Overwhelming, the All-Crushing and the One Who Causes to Die through death and separation. This is, in appearance, not in conformity with the all-embracing Mercy expressed in

My Mercy encompasses all things. (7:156)

Nevertheless, in reality it is conformable with it in several ways, one of which is as follows:

After each group of creatures has completed its turn in the promenade and the desired results have been obtained from it, the All-Munificent Maker, the All-Compassionate Creator, causes most of them, by His Compassion, to feel weariness and distaste with the world, and grants to them a desire for rest and a longing to emigrate to another world. Thus, when they are to be discharged from their duties of life, He arouses in them an enthusiastic inclination to return to their original home.

The Most Merciful One bestows the rank of martyrdom on a soldier who perishes for the sake of performing his duty (in defense of his sacred values), and rewards a sheep slaughtered as a sacrifice in His way by giving it an eternal corporeal existence in the Hereafter and the rank of being a mount for its owner on the Bridge—like Buraq. It is, therefore, not far from His infinite Mercy that, for other animate beings who perish and suffer severe distress while performing their duties, the Lord has assigned in accordance with the nature of each and with their obedience to the Divine commands—it is not unlikely that there should be for them in the inexhaustible treasuries of His Mercy a sort of spiritual reward and a kind of wage according to their capacities, so that they should not be much troubled at departing from the world, rather that they should be pleased. None but God knows the Unseen.

God gives man a longing to go to the eternal world

As for man, who is the noblest of living beings and the one who benefits most from the festivals both in quantity and quality, although he is most captivated by the world and immersed in it, God gives him out of His Mercy a kind of mood whereby he feels distaste with the world and a longing to go to the eternal world. Whoever is not lost in misguidance profits from that mood and goes with a tranquil heart. Out of many reasons that lead to this mood in man, I will explain five by way of examples:

• By showing, according to the season of old age, the stamp of transience and decline on the beautiful and tempting things of the world, and their bitter meaning, the Most Merciful One makes man feel distaste with the world and causes him to seek a permanent beloved in place of a transient one.
• Ninety-nine per cent of the friends to whom a man is attached have departed from the world and settled in another; by enabling in him, through that heart-felt attachment, a longing for the place his friends have gone to, He makes him meet death with joy.
• By means of certain things, He makes man feel the infinite weakness and impotence intrinsic to his nature, and understand how heavy are the burden and responsibilities of life, and grants to him a great wish for rest and a sincere longing to go to another world.
• Through the light of belief, He shows a believer that death is not total annihilation, rather, a change of abode; the grave is not the mouth of a dark pit, it is the door to illuminated worlds; and the world, despite all its glitter, is like a dungeon in comparison with the Hereafter. So, certainly, to be transferred from the dungeon of this world to the gardens of Paradise, and pass from the troublesome turmoil of bodily life to the world of rest and the realm where spirits soar, and to slip free from the distressing noise of creatures and go to the Presence of the Most Merciful is a journey, indeed, a happiness, to be desired most earnestly.
• By making known the knowledge of truth in the Qur’an and the true nature of the world through the light of truth, He explains to the one who listens to the Qur’an that love for the world and attachment to it are quite meaningless. That is, He says the following to man, and proves it:

The nature of the world

• The world is a book of the Eternally-Besought-of-All. Its letters and words point not to themselves but to the Essence, Names and Attributes of Another. This being so, learn its meaning and adopt it, and abandon its decorations, and go!
• The world is also a tillage; sow it and harvest your crop, and preserve it. Throw away the chaff, and attach to it no importance!
• The world is also a collection of mirrors which continuously pass on one after the other. Therefore, know the One Who is manifest in them, see His lights, understand the manifestations of the Names which appear in them, and love the One they signify. Cease your attachment for those fragments of glass which are doomed to be broken and perish!
• The world is also a moving place of trade. So do your business and come; do not weary yourself in useless pursuit of the caravans that leave you behind, paying you no attention!
• The world is also a temporary place of recreation. So study it to take lessons and warnings, and pay attention not to its apparent, ugly face, but to its hidden, beautiful face which looks to the Eternal All-Gracious One. Go for a pleasant and beneficial recreation, then come back, and at the disappearance of the scenes displaying those fine views and showing the beautiful things, do not weep like a silly child, and do not be anxious!
• The world is also a guest-house. Therefore, eat and drink within the limits established by the Munificent Host Who has built it, and offer thanks. Act and behave in accordance with His Law. Then leave it and go away without looking back. Do not interfere in it in a foolish and officious manner. Do not busy yourself in vain with things which part from you and do not concern you!’

Through such plain truths, He shows the real character of the world and makes death less painful. Rather, to those who have awakened to truth He makes death desirable, and shows that there is a trace of His Mercy in every thing and act of His.

So, as well as these five reasons, the verses of the Qur’an also point to some other particular reasons. Woe to him who has no share in the truths contained in these five reasons!