LEXICAL MEANINGS

Islam

In the lexical context, Islam means surrender and submission to the commands of Allah. This meaning occurs in the Qur’an :
("Then, when [Abraham (`alayhi-salam) and his son] had both _submitted_ [to Allah’s command for Abraham (`alayhis-salam) to sacrifice his son], and [Abraham] laid [his son] down on his forehead.") [(37) As-Saaffaat, 103]
Islam also shares the same root as “salam” which is peace, and thus it conveys the meaning of attainment of or bringing about of peace. So, one cannot be a Muslim without submitting unreservedly to Allah and His Messenger, and it is only in this way that one can attain true peace. Anyone who is not content to submit in this way, but insists on hankering after knowledge which is beyond his grasp, and asking questions which cannot really be answered, is veiling himself from true faith and knowledge. Such a person will be confused, suggestible and prone to doubt, vascillating in that manner between faith and disbelief, and between affirmation and denial. Although he is not a believer, yet he is not firm in his rejection either. He ruins and loses his worldly life as well as his Hereafter.
Iman

Iman (belief) lexically means affirmation and confirmation in the heart, as we find in a verse of the Qur’an:
("[Joseph’s brothers] said, ‘O our father! Indeed, we went racing with one another, and we left Joseph with our belongings, and the wolf devoured him. But you will not _believe_ us, even if we are truthful.’") [(12) Yusuf, 17]

("Nay, by your Lord! They do not believe until they appoint you [Muhammad (sallallahu `alayhi wa-sallam)] as judge in those disputes which arise amongst them, and then do not find any resistance in themselves against your decisions, and accept [them] with full submission.") [(4) Al-Nisa, 65]
In this verse, Allah indicates to us the attitude of faith, and that it comprises three things:

1) Resorting to Allah and the Messenger for judgement. Thus, one who resorts to other than Islam for judgement, and considers that valid, is a disbeliever.
“Is it then the judgement of Jahiliyyah (ignorance) that they seek? Who is better in judgement than Allah for a people certain [in faith]?” [(5) Al-Ma’idah, 50]
Imam Ibn Hazm (may Allah have mercy upon him) says, “So, it is not permitted for a Muslim, who affirms Allah’s oneness, to resort in [any] dispute to other than the Qur’an and accounts from the Messenger of Allah (sallallahu `alayhi wa-sallam), nor to refuse what is found in them. If he does that after the proof has been established for him, then he is a transgressor. And, if he does it considering it permissible to depart from their command and enjoining obedience to others besides them, then he is a disbeliever; we have no doubt concerning that.” [Al-Ihkam, 1/99]

2) Not finding any resistance in the heart against the judgement of Allah and His Messenger, so that one will not be uncertain about it, nor imagine that some other judgement is better than it. So, one who is doubtful or suspicious about the laws of Islam is a disbeliever.
“And, when they are summoned to Allah and His Messenger, to judge between them, you see a group of them turning away. Yet, if it had been their right [they were seeking] they would have come to him submissively. Is there in their hearts a disease, or are they doubtful, or do they fear that Allah and His Messenger will deal unjustly with them? Nay, those are the wrongdoers.” [(24) Al-Nur, 48-50]

3) Accepting the judgement and submitting to it unreservedly. The believer must submit to Allah’s laws, and accept them even if he cannot see their exact implication or wisdom.
All of these three stages are imperative in order to have Iman. Then, if the Iman is to be perfect, the believer must, in addition, also submit outwardly by practically carrying out these orders after accepting them.
The Gabriel hadith

On the authority of `Umar (radiallahu `anhu) : While we were sitting with the Messenger of Allah (sallallahu `alayhi wa-sallam) one day, there came upon us a man with extremely white clothes and extremely black hair. No sign of journey could be seen on him, nor did any of us know him. [He advanced] until he sat before the Prophet (sallallahu `alayhi wa-sallam), such that his knees were touching his. He put his hands on his thighs and said, “O Muhammad! Inform me about Islam.” Then, the Messenger of Allah (sallallahu `alayhi wa-sallam) said, “Islam is that you testify that there is no god but Allah and that Muhammad is the Messenger of Allah, [that you] establish salat and give zakat, fast Ramadan and to perform the Pilgrimage to the House [(i.e. the Ka`bah)] if you can make a way thereto.” [The man] said, “You have spoken the truth,” whereupon we were astonished at him, asking [the Prophet (sallallahu `alayhi wa-sallam) and [yet also] confirming him.

He said, “Then, tell me about Iman (faith).” [The Messenger of Allah] said, “That you believe in Allah, His angels, His Books, His Messengers, the Last Day, and that you believe in Destiny, the good of it and the bad of it.”

[The man] said, “You have spoken the truth. Then, tell me about Ihsan (goodness).” [The Messenger of Allah (sallallahu `alayhi wa- sallam)] said, “That you worship Allah as if you see Him, but since you do not see Him, then [know that] He is seeing you.” He said, “Then, tell me about the Hour [of Judgement].” He replied, “The questioned one is not more knowledgeable about it than the questioner.” He said, “Then tell me about its indications.” He replied, “That the slave-girl shall give birth to her mistress, and that you see poor, naked, barefoot shepherds vying in [erecting] tall buildings.”

Then, [the man] left, and I [(`Umar)] remained behind for a while. Then, the Messenger of Allah (sallallahu `alayhi wa-sallam) said, “O `Umar! Do you know who the questioner was?” I said, “Allah and His Messenger know best.” He said, “Indeed, he was Gabriel, who came to you to teach you your religion.” [Narrated by Muslim, Abu Dawud, Tirmidhi and Ibn Majah]

In the above hadith, we find a distinction between the words Islam, Iman and Ihsan. The Prophet (sallallahu `alayhi wa-sallam) has indicated three levels within the religion, the highest being Ihsan, the second being Iman, and the lowest being Islam. Each higher level encompasses those below it, so that the existence of the state of perfect Iman implies the existence of Islam, and similarly, the state of Ihsan embraces Iman. In this sense, every Muhsin (one in the state of Ihsan) is a Mu’min (one in the state of Iman), but the reverse is not always true. Similarly, every Mu’min is a Muslim (one in the state of Islam) without the reverse necessarily following. A Mu’min will necessarily be a Muslim, because he must be practising the five pillars before he can reach the higher state of Iman. In the same way, a person may be performing the five pillars, but may not reach the higher level of Iman.

Similarly, in another hadith, we are told : “The Muslim is one from whose tongue and hand another Muslim is safe. The Mu’min is one whom people trust with their lives and property. The Muhajir (emigrant) is the one who abandons evil. The Mujahid is the one who strives against his self in the obedience of Allah.” [Narrated by Ahmad, Tirmidhi and others] This hadith mentions a total of four levels, each higher than and encompassing the one before it. It is obvious that one who is trusted with life and property will necessarily be such that others are safe from his tongue and hand, for otherwise they would not have trusted him.

It is also obvious that the descriptions given in these hadith are not comprehensive, for one cannot be a Muslim without accepting Islam, even if one is good to others. Nor can one be a Mu’min without belief in the six pillars, even if one is trustworthy. Similarly, if one truly abandons evil, he will physically emigrate from the Land of Kufr to the Land of Islam if he is able to, otherwise he is not a Muhajir. In the same way, striving against one’s self is only one aspect of jihad. If the Muslims are under attack, for example, then sitting at home and trying to fight against one’s self is not enough. The true mujahid is the one who goes and fights for the sake of Allah, for this is the most effective way of fighting one’s desires for life and comfort.

In summary, these levels are subtle and eloquent descriptions based on the lexical meanings of Islam, Iman, Hijrah and Jihad.
SHARI`AH MEANINGS

Notwithstanding the deeper shades of meaning and different lexical meanings, the words Islam and Iman are used interchangeably in the context of the Shari`ah, such that if we refer to someone as a Muslim, it is equivalent to saying he is a Mu’min, and vice-versa. In other words, Islam and Iman are essentially inseparable. Allah tells us about the fate of the People of Lot (`alayhis-salam).
("Then, We removed from it (the town of Prophet Lot) whoever therein was among the believers (Mu’mins). But, We did not find therein other than a single house of Muslims.") [(51) Adh-Dhariyat, 35-36] This house of Muslims which was saved was the house of Lot (`alayhis-salam) (with the exception of his wife who was a disbeliever), and hence the verse indicates that a Muslim is essentially equivalent to a Mu’min (believer).

Similarly, in a hadith, the Prophet (sallallahu `alayhi wa-sallam) said, “I command you to believe in Allah alone. Do you know what belief (Iman) in Allah alone is? [It is] testifying that there is no god but Allah alone, without any partners, and the establishment of salat, the giving of zakat, and the endowment of a fifth of your booty.” [Narrated by Bukhari, Muslim, Ahmad and others] This hadith describes Iman by referring to the pillars of Islam, again confirming the essential equivalence of the terms.

This idea is clarified by the hadith, “Indeed, in the body is a piece [of flesh], such that if it is good, all the rest of the body will be good, whereas if it be corrupted, all the rest of the body will be corrupted. Indeed, [that piece] is the heart.” [Narrated by Bukhari, Muslim, Ahmad and others] So, whoever truly has a good heart must necessarily have a good exterior, although the reverse is not always true.

Imam Sufyan ibn `Uyaynah said, “The scholars in previous times used to write these words to one another : Whoever reforms his heart, Allah will reform his external actions. Whoever makes good that which is between him and Allah, Allah will make good that which is between him and people. And, whoever works for his Hereafter, Allah will suffice him for his world[ly needs].” [Narrated by Ibn Abi’d-Dunya in Kitab al-Ikhlas] In the same light, Imam Abu Hanifah said, “Lexically, there is a difference between Iman and Islam, but [in the shari`ah] there is no Iman without Islam, nor does there exist Islam without Iman, the two being [inseparable], like the inside and outside [of something].” [Al-Fiqh al-Akbar]