The literal meaning of Islam is absolute submission to the will of Allah. The term "religion" reflects God's expectations from mankind in matters related to his individual and social thoughts, conducts and behaviors and also the way he establishes his relationship with God and others. Hence, one who accepts a religion – at any age or time period – must surrender himself to it and when a new religion is sent down by God, the obedient servants are duty-bound, based on the same previous religion, to accept the new religion and surrender themselves to it. Therefore, it can be said that throughout the history of mankind, all the prophets from the first to the last of them had been the preacher of a single religion, Islam. The religion with Allah is only one; there is no difference or discrepancy in it; the difference between various laws was in the degree of perfection, it was not because of any discrepancy or contradiction. All were one inasmuch as all called the people to surrender and submit themselves to the will of Allah, to His commandments sent through His prophets. Although the prophets who were sent to mankind were at different ranks and positions, they all promulgated monotheism and divine unity. One cannot keep following the same old and imperfect divine religion, if there is a new religion which is more perfect as compared to the previous one.[i] Having said that, when the prophets and their Code of law have ended up in the Holy Prophet (s) and the "religion of Islam", and this religion is the global and eternal religion, if someone really considers himself to be religious, obedient and submissive to the will of God, irrespective of whether he is Christian or Jewish, he must accept the pure Muhammad religion so that his belief may be accepted and that he may be rewarded for his good thoughts and conducts and attain heavenly ranks. Thus, after the prophetic mission of the Messenger of God, Prophet Muhammad, peace be upon him and his family, and the perfection of the religion of Islam, no other religion is accepted and no one's deeds are rewarded on the basis of other religions.
[i] -Al-Isra, 55; Al-Baqarah, 253.
Submission to the will of God has different degrees and stages:
1. Creational submission of all beings including humans to God: It means that the creatures and their creational changes, developments their genus (sex) and lastly their deaths have not been relegated to them; all are decided by God and all should surrender themselves to the will, kingdom and dictates of the Lord.
Thus, when it comes to this meaning of submission, even the enemies, pagans, polytheists, unbelievers and hypocrites are willingly or unwillingly, knowingly or unknowingly submissive to the will of God. They cannot disobey God nor can they act against His will.
2. The term 'Islam' means that if man's God-gifted nature is not ill-trained, he is God-seeking by nature. He is totally submissive and obedient to his Creator, Sustainer, Owner and Ruler. He naturally tends towards monotheism and naturally avoids polytheism. Indeed, this is the inward Islam (submission) that elevates Prophet Ibrahim (a.s) to the heavens, and it is because of his monotheistic nature that he called out:
"For me, I have set my face, firmly and truly, towards Him Who created the heavens and the earth, and never shall I give partners to Allah."
3. The third meaning of 'Islam' is religious submission in the sense that humans should act according to divine legislations (obligations and prohibitions) concerning their thoughts, moods and conducts without having to object and without having to discriminate between the educational, practical and moral teachings.
This kind of submission is an essential requirement of 'religiosity'. That is to say, whoever really considers himself to be obedient and adherent to God's religion, he must surrender himself to God's commands and prohibitions even though they are repugnant to his desires and inclinations.
Therefore, if his beloved prophet recommends him to leave, after a while, his Shari'ah to embrace a new code of law which has been brought down by another Prophet and he follows his advice, in this case he is a real follower of his prophet, he is duty-bound to abandon the previous Code of law and act upon the new Shari'ah. To give an example, if the Jews are real followers of Moses (a.s.), they must have accepted Prophet Jesus (a.s.) and embraced his religion. Had they done so, we would not have any Jews in the entire world. The same is true with Christians; if they are the real followers of Jesus (a.s.), they have been commanded to follow, after him, Prophet Muhammad bin Abdullah bin Abdul Muttalib (may peace and blessings of Allah be upon him and his family) and to abandon their altered and distorted religion and become Muslims in the real sense.
4. Islam is the last, the most complete and the most perfect divine religion which abrogates all the religions and faiths before it. No Code of law will come after Islam to abrogate and annul it.
Therefore, following the prophetic mission of the Messenger of Allah (peace be upon him and his family) and the completion of this religion, no religion or code of law will be accepted from anyone because God does not consent to any other code of law after Islam. That is why belief in Prophet Muhammad (s) and submission to this religion requires belief and affirmation of other codes of law and prophets plus their complements and supplements (new and updated rules and teachings). However, belief in other codes of law is belief in a religion which cannot meet the human needs to attain prosperity in this world and in the hereafter. They are deficient from this perspective and God does not want us to believe in them or act upon them. Therefore, those who believe in them and practice them will not be given any reward. Moreover, the previous religions have been distorted and they are not the same religions that were revealed to the prophets.
The term "al-Islam" in the said verse can include the aforementioned four meanings because man should naturally choose his own way and shape his fate. He should reply to the inward natural call in the positive because this religion is in accord with man's God-gifted nature and his sound reason. In fact, he who accepts this religion also accepts other religions and prophets. He knows that they were definitely the prophets of God and promulgators of his true religion as well as the leaders of humanity guiding them to perfection. Thus, the undistorted religion which they had brought fourth paved the way for presentation of the most complete and most perfect of all religions, i.e. the religion of Islam which has characteristics and features that other religions lack. Thus, it is only through following this religion that a man is said to be submissive to the will of God and adherent to His right path.
The next point to mention in this regard is that there are different degrees and stages in accepting this religion. They are enumerated and explained as follows:
1. Apparent conversion of Islam by saying the "Two Testimonies" (Shahadatayn) and apparent acceptance of divine commandments which may not be sincere and genuine. The direct impact of such a conversion is that he who accepts Islam apparently is treated as Muslim in areas like marriage, transactions, purity of body, clothe and respect of his life and property.
2. Genuine acceptance and embracement of the entire divine teachings of Islam on the part of an individual who may commit some practical offense or entertain scientific hesitation or do an action with reluctance.
3. Islam in the wake of genuine acceptance and sincere faith in the religion and in the Holy Prophet, peace be upon him and his family, resulting in submission of both the heart and mind as well as the limbs to the Lord, the Prophet (s) and Imams as well as their commandments and prohibitions without entertaining the least doubt or having the least reluctance in accepting and fulfilling them. Thus, the servant considers himself as being owned by God, the Exalted, and considers God as his owner. Thus, he prefers His satisfaction and pleasure over his own pleasure and he does what he thinks God wants him to do.
4. Islam means to surrender oneself to the will of God in a way such that one does not consider an iota of independence or free will for himself. This is absolute submission in the sense that one does not will except that which is willed by Allah. He does not do anything except that which is commanded by Him. He puts all his efforts into gaining the pleasure of Allah. He endeavors in this way until he attains the position of the noble saints of Allah, those who are not afraid of anything nor are they worried;  they do not regret their past and what they have lost nor do they worry about their future; because they have attained the position of etminan (certitude); they are only waiting for God to invite them so that they meet him. In this way, whatever happens to them is welcome even if it be an incident like the incident of Karbala!
Therefore, the "true Islam" is that which bears all these degrees and traits. For this reason, the Holy Prophet's submission is not comparable with others' . The same is true with the submission of the Infallible Imams, peace be upon them, whose faith and adherence are not comparable with others. The evidence and indications are too many to be enumerated in this regard. If one is a truth-seeking researcher, he himself should go through sirah and history books to find about the Infallibles' submission.
In short, absolute submission to the truth requires acceptance of Islam and acceptance of the religion of Islam requires absolute submission to God. This delicacy rests in the meaning of the word "submission". Every meaning in the word is a concomitant of the other meanings.
On the other hand, the religion of Islam was perfected with 'wilayah' i.e. the appointment of Imam Ali, peace be upon him, as the successor to the Prophet (s) and leader of the Ummah. One who denies the wilayah is not submissive to the command of God; he has not accepted the true Islam (religion in its perfect sense) and while following the Shari'ah, he has acted only on some codes and ignored some others whereas God, the Glorified, says:
"O ye who believe! Obey Allah and His Messenger, and turn not away from him when ye hear (him speak). Nor be like those who say, "We hear," but listen not: For the worst of beasts in the sight of Allah are the deaf and the dumb,- those who understand not. If Allah had found in them any good. He would indeed have made them listen: (As it is), if He had made them listen, they would but have turned back and declined (Faith). O ye who believe! give your response to Allah and His Messenger, when He calleth you to that which will give you life; and know that Allah cometh in between a man and his heart, and that it is He to Whom ye shall (all) be gathered. And fear tumult or oppression, which affecteth not in particular (only) those of you who do wrong: and know that Allah is strict in punishment. Call to mind when ye were a small (band), despised through the land, and afraid that men might despoil and kidnap you; But He provided a safe asylum for you, strengthened you with His aid, and gave you Good things for sustenance: that ye might be grateful. O ye that believe! betray not the trust of Allah and the Messenger, nor misappropriate knowingly things entrusted to you.
Also, he said:
Say, "The truth is from your Lord": Let him who will believe, and let him who will, reject (it): for the wrong-doers We have prepared a Fire whose (smoke and flames), like the walls and roof of a tent, will hem them in: if they implore relief they will be granted water like melted brass, that will scald their faces, how dreadful the drink! How uncomfortable a couch to recline on!
There is no doubt that the 'Quran' and 'Itrah' (household of the Holy Prophet) are weighty and invaluable things entrusted to us. The Holy Prophet of Islam, peace be upon him and his family, called on all Muslims to turn to these two and seek help from them. He said that the Quran and Itrah remain together until the Day of Judgment. Hadith Thaqalayn is famous among Shia and Sunni and it is considered as a 'mutawatir' (narrated by many narrators) report. Therefore, Islam without belief in 'wilayah' is not a real Islam and God will not be pleased with it.
1. Shirazi, Mirza Abu Talib, Israr al-Aqaed, Maktab al-Islam, 1st edition, 1377 (1998), Qom (the entire book and also the interpretations under the verses mentioned in footnotes).
2. Tabatabai, Muhammad Hussein, Al-Mizan, Islamic Publications, Qom, vol.1, pp. 300 – 308, vol.7, pp. 342 – 347, vol.3, pp. 121 – 123 and 331 – 339.
3. Qommi Mashhadi, Muhammad bin Muhammad Reza, Kanz al-Daqaeq, Ministry of Guidance Printing and Publication Institute, 1st edition, 1411 A.H., Tehran, vol.4, pg. 123 and 442 and vol.3, 56 – 58.
 - Aal-e Imran, 83, Al-Ra'd, 15, Fussilat, 11.
 - Vide: Index: "Freedom and Divine Will", question 153, Al-Ankabut, 98.
 - Al-An'am, 79.
 - Al-Ahzab, 36; Al-An'am, 122- 127; Al-Nisa, 60 – 70.
 - Al-Ahzab, 40; vide: Mutahhari, Murteza, Finality.
 - Aal-e Imran, 79 – 95.
 - Al-An'am, 153; Al-Maedah, 15 – 19.
 - Al-Hujurat, 144.
 - Al-Zukhruf, 69; Al-Baqarah, 208; Al-Hujurat, 15.
 - Al-Nisa, 65; Al-Momenoon, 1 – 3.
 - Yunus, 62
 - Al-Hadid, 23; Aal-e Imran, 153
 - Al-Fajr, 27 – 30.
 - Vide: Tafsir al-Mizan, vol.1, pp.300 – 303.
 - Vide: Index: "Alteration and Non-Shi'ah Religions", question 260; Al-Maedah, 3 and 67.
 - Al-Anfal, 20 – 27.
 - Al-Kahf, 29.