Answer
Salam Dear Brother,
Thank you for your question and for contacting Ask About Islam.
The quick answer to your query: No, a Muslim is not allowed to convert to Christianity or any other religion for that matter. Apostasy is a major sin in the sight of Allah, Who says in the Quran what means:
{This day have I perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion.} (Al-Maidah 5:3)
In other words, Islam is the final, perfected form of Allah’s single, universal truth that came on the tongue of every prophet, including Jesus. Why then should we give up the final religion for the sake of a religion that, though originally pure and perfect, has been tampered with by the hands of humans, both well-intending and otherwise.
To phrase it in another manner, every true prophet of God came with the same message: God is singular, with no partners; this world is fleeting and deceiving while the hereafter is grave and eternal.
Wake up! The legal systems they brought, however, differed according to the period in which they were sent. Thus, Jesus’ law, which was Jewish law in fact, would be inappropriate for the modern world, which is one reason why you won’t find a single Christian practicing it.
Beyond jurisprudential matters, when we compare the “mainstream” (as opposed to capricious) understandings of God in the Islamic and Christian religions, we see major areas of departure that cannot be reconciled into an “everybody’s right” approach.
For example, the concept of God’s having a son is completely unacceptable from the Islamic standpoint, as Allah says in the Quran what means:
{They say: “The Most Gracious has betaken a son!” Indeed you have put forth a thing most monstrous.} (Maryam 19:88–89)
And two verses later, Allah explains what means:
{For it is not consonant with the majesty of the Most Gracious that He should beget a son. Not one of the beings of the heavens and the earth but must come to the Most Gracious as a servant.} (Maryam 19:91)
Similarly, for a Muslim to forgo the teachings of Muhammad (peace and blessings be upon him) in exchange for the altered form of an earlier prophetic message is akin to trading gold coins for wood chips, only it is a sinful transaction because we are infringing upon the rights of God, our Creator and Sustainer.
Islamic sacred law is clear in its appointing special rights and dignities to Jews, Christians, and recipients of other divine texts who are living within a Muslim state.
The Muslims are required to make many concessions to “the People of the Book” (Jews and Christians) to ensure a peaceful co-existence and a successful civilization. However, this must not be interpreted as a tacit acceptance of their religious beliefs with regard to the eternal life of the hereafter.
A Muslim cares for his Christian neighbor as a human being; he treats him with excellence and hopes and prays for his success in both this world and the next. However, a Muslim does not believe that his Christian neighbor’s religion is Truth, nor a viable path to God’s pleasure.
With this in mind, should a Muslim leave Islam or convert to any other religion after having attained a true understanding of the Islamic precepts, he has committed a major infraction of Islamic sacred law and is urged to rethink his weighty decision.
Naturally, Islam’s condemnation of apostasy does not reconcile with the religious relativism and unqualified pluralism that are common in the modern Western world. It must be kept in mind that the reality of God is one, and it is logically impossible for a Muslim, Jew, Christian, and Buddhist to ALL be correct on an absolute level in their theological understandings.
The tendency of modern, secular society is to sidestep theological differences so that we can all focus on “just being good people.” This is a consequence of the atheistic trends that have thoroughly integrated themselves into all levels of society.
The proponents of such an attitude are, in effect, mocking people of religion, essentially saying, “Yes, yes, you’re free to believe in a ‘God,’ just don’t do it publicly and don’t think that your beliefs are Truth.”
Ironically, the religious naysayers cite bloodshed in the name of religion as their historic proof for the excellence of unqualified religious pluralism, while the “secular” wars of the past two centuries have resulted in far more bloodshed and oppression than all “religious” wars that preceded them.
In fact, absolute religious pluralism (as distinct from qualified pluralism that yields religious harmony without compromising a religion’s exclusive claim to Truth) is dismissed as ridiculous and illogical by the vast majority of humanity, while its chief proponents are often agnostics and other people with little or no religious practice in their daily lives. Admittedly, there are many exceptions to these trends.
In finishing, Islam is clear in its condemnation of apostasy, and I cannot sugarcoat this fact simply because it conflicts with your ideals. On the other hand, I urge you to reflect upon your initial shock and consider the logic of this ruling as we have discussed above.
While I want nothing more than for every Christian in the world to become my brother and sister in Islam (including you), I nonetheless expect the teachings of Christianity to condemn those who leave the church for another religion.
Thank you for your question and please stay in touch.
Salam.