Compulsion is contrary to the meaning and purpose of religion, which essentially is an appeal to beings endowed with free will to affirm and worship their Creator. Intention and volition are necessary bases of all actions (including formal worship), attitudes, and thoughts for which the individual is religiously accountable. Without that basis, accountability has no meaning. According to Islam, actions are not considered religiously acceptable or valid unless they are done with the appropriate intention. Compulsion also contradicts the religious–legal principle that actions are to be judged only by intentions.
Islam does not allow Muslims to be coerced into fulfilling its rites and obligations, or non-Muslims to be forced into accepting Islam. Under Islamic rule, non-Muslims always are allowed full freedom of religion and worship if they agree to accept Islamic rule. This is indicated by their payment of jizya (capitation tax) and kharaj (land tax). In return, the state protects their lives, property, and religious rights.
The Islamic way of life cannot be imposed or sustained by force, for faith (iman) is essential to it. And as we know, faith is a matter of the heart and conscience, both of which are beyond force. In the absolute sense, therefore, compulsion is impossible, for one can believe only with and from the heart.
From the time of Adam, religion has not coerced anyone into unbelief or forced anyone to stray from righteousness. However, the powers of unbelief always seek to coerce believers away from their religion and their faith. No believer has tried to coerce an unbeliever to become a Muslim, whereas unbelievers continually try to lead believers back to unbelief.
Some ask why some Qur'anic verses describe fighting and jihad as obligatory, on the grounds that this appears to sanction compulsion.
Fighting and physical jihad were commanded because, at that time, the unbelievers fought the believers in order to eradicate their religion. The command to fight enabled and established an ethos that recognizes the right of religious freedom and extends it to all. In other words, Islam understands and practices the principle of "there is no compulsion in religion." Muslims had the confidence and self-assurance to understand that once that principle becomes part of the collective ethos, people will recognize Islam's truth and enter it of their own will. Historically, that is what happened throughout the territories under Islamic rule and, of course, far beyond.
We can look at this matter from another perspective. The command to wage war against unbelief pertains to certain circumstances. As civilizations rise, mature, decay, and fall, similar or the same circumstances will occur and recur. Tolerance and letting-be will be replaced by persecution, which calls for force to re-establish religious freedom. At other times, the attitude expressed in: To you your religion, and to me my religion (109:6) will be more appropriate.
The present is a period of the latter sort, one in which jihad is seen in our resolution, perseverance, forbearance, and devoted, patient preaching. And so we teach and explain. We do not engage in coercion, for there would be no benefit in our doing so. The misguidance and corruption of others is niether the target nor the focus of our efforts. We provoke, target, or offend no one. But, we try to preserve our own guidance in the face of misguidance. And in our own lives, we strive to establish the religion.
Just because a particular Qur'anic command is not applicable in present circumstances does mean that it is no longer applicable or relevant. Rather, it means that the command can be applied correctly or properly only in certain circumstances. We do not know when such circumstances will recur, only that they will. Meanwhile, the principle underlying the command remains relevant and applicable: religious persecution is abhorrent at all times and in all places. In the law and history of Islam, this principle has meant that under an Islamic polity, no non-Muslim can be coerced to enter the faith, and that all persons are free, both individually and communally, to live their faith.
Even non-Muslim, Western scholars, who often are hostile to Islam, acknowledge that Jews, Christians, and other non-Muslims ruled by Muslims generally enjoyed much greater economic prosperity, dignity, and prestige, and had far more freedoms than under non-Islamic rule—even that of their own co-religionists. Nor did this situation change significantly in the Western world until a through-going secularization diminished the importance of religious beliefs, rites, and solidarity. Intolerant states did not become legally tolerant so much as legally indifferent.
Religious tolerance is, in some sense, a sociopolitical characteristic special to Islam, one derived directly from the Muslims' understanding of and commitment to the Qur'anic principle of "there is no compulsion in religion."
Even in modern times, Western political constitutions typically make space for individual religious freedom, as opposed to collective and communal religious freedom. The Islamic polity recognizes the relevance and importance of community to the practice and continuance of religious beliefs and traditions. That is why, in lieu of jizya, Muslims protected the lives and property as well as the rites and places of worship of their non-Muslim subjects. Also, non-Muslims were recognized as distinct communities with their own schools and institutions. The conditions for such a display of successful religious pluralism were a just, impartial central authority and the discipline of non-provocation. A collective ethos of tolerance cannot be sustained without that discipline. For example, neither Muslims nor non-Muslims were allowed to blaspheme or otherwise mock and undermine each other's beliefs and rites.
Such disciplines and the related deterrent sanctions do not amount to coercion and compulsion. Islam also applies Muslim-specific deterrent sanctions to maintain the Islamic social order and ethos. An analogy may clarify this point. Most states have armed forces. These forces are composed either of volunteers or conscripts. Both types of soldiers are governed by the same disciplines (and sanctions). There is no "conscription" into Islam, for you can enter only by repeating the shahada. To be valid and acceptable, this declaration must be voluntary and sincere. After that, the duties and obligations of Islam apply equally to all Muslims.
Of course, the system and its discipline is not external and as rigid as an army discipline is and has to be. Nevertheless it is a discipline, and breaches entail sanctions based on the seriousness of the matter. Typically, the disciplines of Islam are acquired gradually. Due to their inherent naturalness and ease and, most especially, because they are based on Divine and not human commands, they are readily internalized and welcomed in the heart.
When a sergeant shouts "Attention!" at his soldiers, they jump to a command that is always and only external—one obeys only because one must. By contrast, when the leader of a Muslim congregational prayer calls Allahu akbar, everyone present gives himself or herself the same command—it is internal as well as external. One obeys because one wants and consents to do so, and one is glad that one must. The solidarity and cohesion of a Muslim congregation (as the variety and rhythm of its members' movements demonstrates) is the solidarity of individuals gathered by consent to share in the same noble endeavor. Each fulfils his or her duty a little behind or a little ahead of another, but still together with all. It does not look like, nor is it, the mechanical solidarity of uniformed soldiers on parade.
Unsurprisingly, most breaches of discipline are slight, informal, and informally put right—usually by one Muslim advising a fellow Muslim to do the right thing and stop doing the wrong thing. Elaborating, exaggerating, or even reporting on someone's shortcomings or sins of others is considered a grave fault in Islam. Forbearance, forgiveness, patience for others, strictness for oneself—this is the more commended and generally practiced stance of the overwhelming majority of Muslims.
However, certain kinds of breaches threaten the social ethos as a whole. If such threats are not countered, the social ethos becomes eroded and society's general order and stability is undermined. Where informal private efforts to correct matters right have failed or are of no use, formal public measures, including force, must be applied. For example, Islam forbids the consumption of intoxicants, gambling, adultery, fornication, fraud, theft, and other harmful practices. It considers them both sins and crimes subject to punishment. If these vices are allowed to take root and spread, society has failed to fulfill its duty to the law and moral ethos of Islam. Collective action must be taken to prevent or undo widespread corruption within the social body. While such action includes positive efforts to educate the community in the corresponding virtues, it also must accept the negative action of imposing appropriate penalties on those who wilfully and systematically introduce vices into society that will destroy its discipline and Islamic character.
Certain religious rulings have been formulated for the purpose of deterring people from sin. They should not be considered as “compulsion,” for these rulings are binding only on those who have entered the fold of Islam and accepted these rulings in the first place with their free will. We may consider the issue of apostasy here. Traditional Islamic law accepts apostasy as a crime and if that person does not repent, the penalty has been determined to be execution. This is not to impose upon, or deprive thereof, a certain form of belief, but in relation to that person’s violation of a previously agreed contract with the legal system of the governing body he or she happens to be. Such rulings on apostasy were designed to protect the system that constituted the state administration. It would not be possible to talk about a state administration should it be manipulated based on personal aspirations, accepting it one day and renouncing the other day. Thus, we may conclude that traditional rulings on apostasy were political in nature taken as a measure to protect and maintain state administration; they were not religious rulings per se.
"There is no compulsion in religion" because we have free will and because "Truth stands clear of falsehood." Truth has an absolute authority within the human conscience, which calls it urgently to affirm its Creator and Sustainer. In both individual and collective life, the Truth's absolute authority demands a flexible but strong and steady discipline. Discipline and forbearance, as well as compassionate understanding and patience, are the proper responses to all breaches—but only up to and until the discipline itself is threatened with destruction. Like every discipline, the discipline of Islam imposes its burdens. But unlike any other, the rewards for carrying those burdens with sincere devotion are sanity, serenity, and ease in this life and in the life to come.
 Bukhari, Bad' al-Wahy, 1; Muslim, Imara, 155; Abu Dawud, Talaq, 11.
 Traditionally, the jizya was not levied on non-Muslims who participated with Muslims in military engagements.
 The Muslim profession of faith: "There is no god but God, and Muhammad is His Messenger." After reciting this statement, a person is considered a Muslim and a member of the Muslim community.
Editor’s Note: The following update offers additional context to the last three paragraphs of this response and clarifies Fethullah Gülen’s views on apostasy.
“Everyone has the right to freedom of religion and conscience. This right includes freedom to change one’s religion or belief, to worship individually or collectively, and to express one’s beliefs through teaching or practicing.”