.
"Verily Allah chose Adam, Nuh, the family of Ibrahim, and the family of `Imran over all people."[24]

.
"Say: Praise be to Allah and peace be with those of His servants whom He has chosen."[25]

.
"O’ Maryam! Verily Allah has chosen you, purified you, and chosen you over all the ladies of the world."[26]

.
"Surely Allah has chosen him over you."[27]

.
"(O’ Musa) verily I have chosen you over mankind with my communications."[28]

.
"Then We gave the book in inheritance to those of Our servants whom We had chosen."[29]
Even Mansur, the â€کAbbasid caliph, would say that Imam Jaâ€کfar al-as-Sadiq (peace be upon him) was among those denoted by the verse:

"those of Our servants whom We have chosen."[30]

.
"And verily We chose him in this world."[31]

.
"Allah chooses messengers from among the angels and mankind."[32]

.
"And verily with Us they are from among the chosen and righteous ones."[33]

.
"And from among those whom We guided and chose."[34]

.
"And We chose them and guided them."[35]

.
"But Allah chooses whom He wishes among His messengers" (and conveys to them those hidden realities which are necessary for their leadership position).[36]

.
"Allah chooses whomsoever He wishes."[37]

.
"And thus does thy Lord choose thee."[38]
… and many more verses, all of which indicate that selection is one of the acts of Allah in His wisdom, or rather is one of the Divine manners of conduct.
There is a treatise by Zaid al-Shahid, the son of Imam Zain al-â€کAbidin (peace be upon him), called al-Safwah in which he has studied the issue of the selection of the Ahl al-Bait.
The issue of granting rank exists in the natural world as well, and its necessity is entirely understandable by reason. Just as all species cannot belong to the human species, and all organs cannot be the eyes or head or brain, and all fruits and plants cannot be berries and squash, and the entire tree cannot be the branch, leaves, or roots, in the same way, all individuals cannot be perfect in their manners, qualities, and features. That is, all cannot be Muhammad (peace be upon him and his family), â€کAli (peace be upon him), Ibrahim al-Khalil (peace be upon him), or Musa al-Kalim (peace be upon him).
The issue of being an Imam or a follower (ma’mum) as well is such that it is either through Allah’s decree and natural causes or through direct specification and selection by Allah. In any case, all of these are signs that are laden with secrets and wisdom which only Allah Himself knows.
In these affairs none has the right to say, "Why was I not made into someone or something else?" or, for example, "How come all the angels were not made Jibra’il al-Amin (the Trustworthy) and all people were not made Muhammad al-Mustafa (the Chosen)?" or "Why weren’t all of the world’s mountains and rocks made of gold?" If such a thing were to happen, the perfection of the world would become subject to defect and the order and coordination existing among its various parts would cease to exist.
This is though the Noble Qur’an itself speaks thus about the order and minute coordination existing among the parts of the universe:

.
"And the sun travels in its appointed path; that is the decree of the Mighty, the Knowing. And We have appointed phases for the moon until it becomes like an old, yellow, date branch. Neither is it appropriate for the sun to overtake the moon, nor does the night overtake the day; and all float in their orbit."[39]
"Everything in the world is in its place—
If you look well, nothing is more or less
All Divine decrees are just and wise—
Our intellects can’t fathom the secrets of creation"
While the human world is a world of choice and selection, the secrets of these matters – i.e. Divine decrees and selection are so complex that it can be said that even if humanity were to conduct research and studies for millions of years to come, they would still be faced with many unknown secrets.
In summary, the world of creation is a world of causes and effects, and at the same time the human world is a world of choice and duty.
The wise Divine decrees and ordinances govern all affairs. Understanding the reasons for selection of an Imam or prophet and its creational and discretionary aspects, and other such issues, requires an intimate knowledge of all the secrets of Divine actions and the universe. Only those who have come under Allah’s special guardianship understand the fine points of these matters, and all of the prophets and Imams (peace be upon them) were as such.
All human individuals have been encouraged by various means to strive to gain mastery over the sun and moon, and so forth, and since Allah has made them subservient to humanity, they can try to comprehend the secrets of things and make use of their benefits; but if they are unable to understand something’s cause or causes, they must regard it as a Divine decree and make use of its existential blessings.
Thus, it is our duty to make use of the teachings and guidance of the prophets and Imams (peace be upon them) and regard the blessing of their existence and guidance among the greatest of Divine blessings and make them our role-models. And if we are unable to comprehend the philosophy of the selection of these true Divine proofs with our imperfect intellects, we must not turn to rejecting or opposing them. Otherwise, we will be regarded as among those people who in the era of the Prophet (peace be upon him and his family) himself denied – either out of ignorance or with ulterior motives – that the selection of the progeny was Divine. The Noble Qur’an, in the course of a verse, mentions them as follows:

.
"Or are they envious of the people (the Prophet and his progeny) on account of what Allah has granted them out of His abundance? Verily, we granted the family of Ibrahim the Book and wisdom and granted them a great kingdom."[40]
According to the Qur’anic commentaries, this verse was revealed about them. It is incumbent upon us to understand, through reflection and contemplation of the circumstances of the universe, that everything is found in its particular place and the Divine knowledge and wisdom is evident in all of the great and small creations of the Lord of the Universe. Therefore, precisely as we read in one of the verses of the Noble Qur’an,

.
"Allah best knows where to place His messengership."[41]
Thus, selection of the prophets and Divine legatees is among the affairs that, like all the other actions of the Lord of the Universe, are possessed of their own particular wisdom, though humanity with its imperfect knowledge and intellect may be unable to fathom its secrets and complexities.
Notes:
[24] Surah Ali-Imran (3), Verse 33
[25] Surah al-Naml (27), Verse 59
[26] Surah Ali-Imran (3), Verse 4
[27] Surah al-Baqarah (2), Verse 247
[28] Surah al-A`raf (7), Verse 144
[29] Surah al-Fatir (35), Verse 32
[30] Surah al-Fatir (35), Verse 32
[31] Surah al-Baqara (2), Verse 130
[32] Surah al-Hajj (22), Verse 75
[33] Surah Sad (38), Verse 47
[34] Surah Maryam (19), Verse 58
[35] Surah al-An`am (6), Verse 8
[36] Surah Ali-Imran (3), Verse 179
[37] Surah ash-Shura (42), Verse 13
[38] Surah Yusuf (12), Verse 6
[39] Surah Yasin (36), Verses 38-40
[40] Surah an-Nisa’ (4), Verse 54
[41] Suurah al-An`am (6), Verse 124