.

Explanation
If we were to ask a student: Why do you study? He would say: So that I can gain admission into a university.
If we ask: Why do you desire to get yourself admitted into a university? He would answer: So that I can become an able doctor or an engineer (for example).
If we ask again: Why do you desire to possess a medical or an engineering degree? He shall say: So that I may engage myself in a productive activity and also that I earn a good income.
If we were to persist and ask: Why do you need a good income? He would say: So that I can lead a respectable and comfortable life.
Finally if we ask him: Why do you desire to lead a respectable and comfortable life? At this juncture we shall notice that his tone changes and he will say: Well, so that I can lead a respectable and comfortable life.
He repeats his previous answer.
This proves that he has reached his final answer and, technically speaking, he has reached the أ›أ³أ‡أ­أ³أ‰أµ أ‡أ،أ؛أ›أ‡أ³أ­أ‡أ³أٹ - the final aim of his efforts beyond which there exists no answer and which constitutes his final aim and objective. This is with regard to the material life.
The case is similar in respect to the spiritual life too. When it is said: What was the purpose of the prophets, the revelation of the Divine Books, the religious obligations, and the educative set-up? We say: For achieving human perfection and attaining proximity to Allah (s.w.t.).
Now, if it is said: What is the purpose of achieving human perfection and attaining proximity to Allah (s.w.t.)? We say: For proximity to Allah (s.w.t.)!
This is the final aim. Expressing it differently, we desire everything for the sake of perfection and attaining nearness to Allah (s.w.t.), but we seek nearness to Allah (s.w.t.) for itself (i.e. nearness to Allah (s.w.t.) ).[4]
Notes:
[4] Tafsir-e-Namuna, vol. 22, pg. 393

Why does Allah (s.w.t.) test people?
The topic of Divine trial is an issue of great debate and discussion. The first question that comes to mind is: Are trials not for understanding matters which are obscure, hence eliminating our ignorance? If so, why does Allah (s.w.t.), Who possesses knowledge of the hidden and the manifest of everything within the heavens and the earth, have to examine and test (the people)? Does there exist something, which is concealed from Him and which may become manifest for Him by means of examination?
The answer lies in the fact that the concept of examination with respect to Allah (s.w.t.) is vastly different from that, with respect to us.
Our examinations are that which has been stated above, i.e. for a better comprehension and for clearing away ambiguity and ignorance, whilst the Divine trials are, in reality, development and training.

Explanation
In the Noble Qur`an there are more than twenty instances of examinations that have been attributed to Allah (s.w.t.). This is a general law (of conduct) of Allah (s.w.t.), implemented by Him for the development of man's hidden abilities (and bringing them from potentiality into actuality), thereby enabling him to progress. Just as iron, for acquiring greater strength, is put into a furnace to make it tempered, similarly man is also nurtured within the furnace of adversities in order that he becomes steadfast.
In reality, the examination of Allah (s.w.t.) resembles the work of an experienced gardener, who sows the seeds in a fertile soil. These seeds, benefiting from the natural bounties, begin to grow gradually - combating adversities, battling unfavourable conditions and enduring violent storms - until they end up in the form of a spray or a copious gargantuan tree, capable of continuing their existence in the face of hardships.
For the purpose of making soldiers tough, militarily, they are made to participate in numerous different exercises and war games, wherein they are subjected to various hardships such as hunger, thirst, heat, chillness, adverse conditions and severe obstacles, in order that they develop into accomplished, conditioned and proficient soldiers.
And this is the secret of Divine examinations.
The Noble Qur`an has asserted this reality, when it says:
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“And that Allah (s.w.t.) might test what was in your chests and that He might purge what was in your hearts; and Allah (s.w.t.) knows what is in the hearts.â€‌[5]
The Commander of the Faithful (a.s.), in a statement very profound in meaning regarding the philosophy of Divine trials, says:

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“Although Allah (s.w.t.) s more aware of their souls than they themselves are, He tries them so that their deeds, which necessitate reward and punishment, become manifest.â€‌[6]
Accordingly, the internal attributes of man can only be a measure for reward or chastisement when they manifest themselves in man's actions. Allah (s.w.t.) tries man to enable that which he possesses in the interior to become manifest in deed and, his talents and abilities emerge from potentiality into actuality.
In the absence of Divine examination, these talents and abilities would have never flourished, and consequently the fruits of deeds would have never manifested themselves upon the branches of the tree of human existence; and this is the philosophy of Divine trials from the Islamic perspective.[7]
Notes:
[5] Surat Ale 'Imran (3), Verse 154
[6] Nahjul Balagha, Short Saying 93
[7] Tafsir-e-Namuna, vol. 1, pg. 526