Although the eternal source and the ultimate objective of religion is nothing but God, different Shari’ahs have, in the position of declaration and proclamation, been established or presented over time as per the requirements of time, human capacities and need for prophetic guidance. This trend of proclamation continued until the most perfect and most complete religion or Shari’ah was brought down by the Last Prophet – peace and benedictions of Allah be upon him.

Religion in this position refers to the instructions that guarantee man’s protection in this world and the next. These instructions, which show the way to prosperity and salvation at every age, have been sent to mankind and declared through revelation.

Before we embark on explaining the differences among the religions, it is necessary to know in the beginning that, according to Islam, human beings have a single fitra (nature) and that tribal, racial, temporal and geographical differences are external differences only. Therefore, if human beings are supposed to have a single nature, obviously the way to their salvation would also involve permanent and unchanging elements and principles.

The unchanging and eternal Shari’ah which is from God is materialized as a static reality regardless of the differences which originate in environment, history, race etc. Eternal religiosity is the focus of all divine prophets’ attention; it is something which corresponds with the God-gifted nature. What is certain is that the need of mankind for guidance has not been the same at all times and ages. The differences existing among various religions are due, largely, to the same reason. In order to clarify the various aspects of this discussion, we can elaborate briefly on the different stages of religion. These stages which begin from the permanent source of religion and continue until the “common religion” stage can be divided into four parts:   

1. 1- The “nafsul-amr” religion: What exists in the knowledge of Allah (swt) regarding the guidance of man to his eternal prosperity and salvation, is the “nafsul-amr” religion. In other words, the nafsul-amr religion is the way of life for man from the beginning to the end. The nafsul-amr religion is the “prescription” and the guidelines to the salvation of mankind which is in the Al-Lawhul Mahfudh (the preserved tablet; referring to the knowledge of Allah (swt)). The nafsul-amr religion is an entity of true reality that has its own existence and isn't something merely imaginary without any reality.[1]

2- The “mursal” religion: The religion that has been sent down to man for his guidance through his prophets. In other words, the “mursal” religion is a portion or all of the “nafsul-amr” religion which is bestowed upon man via the prophets.

3- The unveiled (makshoof) religion: What is revealed and unveiled from nafsul amr or mursal religion for people by way of referring to reason and narration is the “makshoof” religion.

4- Institutionalized “religion”: The part of unveiled religion which becomes public and is institutionalized and which turns into faith of a group of people is the “institutionalized” religion.[2]

To further explain the above, since mursal religion is brought down by prophets, its characteristics and level depend on the characteristics of the messenger in terms of the spiritual level and characteristics of people and temporal as well as geographical limit of his message. The loftier a messenger’s position, the more he benefits from nafsul amr religion, albeit through revelation. Similarly, if people or those who are the addressees of the message have more cultural ability and reception capacity, they will benefit from nafsul amr religion through narration. The greater the temporal and spatial capacity and the more places the message of the religion is sent out to and the more the addressees in different times, the more elements will the mursal religion contain of nafsul amr religion.

Having said that, the last religion which was brought down by the best and last of prophets and whose addressees are people from the time of revelation until the Day of Judgment, must be the most complete religion and must incorporate all what is explained from the nafsul amr religion through revelation or narration.[3]

It has been made clear from the foregoing explanations that, as per the terminologies which were mentioned in the question, the accepted viewpoint in this regard is the evolutionist approach.

Therefore, Islam is a religion which addresses man’s God-gifted nature and encompasses all nations and tribes in the entire eras after the emergence of Islam. For this reason, the followers of all previous religions have also been invited to Islam. It is for the same reason that most of the truth-seekers of the world who are capable of overcoming the barriers and hurdles to the reality – regardless of their religious affiliation – have finally understood the truth and introduced Islam as the true religion.

The emphasis on the lofty reality of Islam can serve as a prelude to understanding and getting acquainted with the lofty realities of Islam; otherwise, if it were meant to keep every individual in his religion and the inherited traditions, it would amount to remaining in the same level of imperfect awareness. According to this supposition, no special mission is presumable for Islam as the last divine message and finality also cannot have any logical analysis.

Some mystics’ sayings about the divine realities of prophets which somehow refer to "oneness in manyness" (wahdat dar kathrat) never consider all the divine religions as one especially in view of the fact that many of those religions have undergone numerous changes and alterations. In fact, those mystics were aware of the special place of the Muhammadan Islam and they underscored the need for its propagation and promulgation. However, their expressing love and respect for the divine position of all human beings and also their conduct which somehow indicate their respect for the followers of all divine religions do not imply the righteousness of every religion.

According to mystics, all men are in search of absolute truth, absolute power and absolute knowledge which are prerogative of God, the Exalted.  All the religions are expressions of human reality. Some mystics’ sayings including this: “There is monotheism concealed under infidelity”[4] refer to the very fact and it does not imply righteousness of all religions.

Therefore, when it comes to mystics’ remarks and sayings, one cannot ignore most of them or pass judgment about them outright or consider some of them as confirmation of special views about Islam or other religions.