Holding fast to the rules of Islam

Question: After learning my religion correctly, I have begun to observe its rules as much as I possibly can. An atheist heard about my situation and emailed me so: “I heard about your becoming an extremist. You are said to perform namâz, observe fast, and cover yourself. By doing so, do you count yourself a better Muslim? It suffices to have a pure mind-set and heart. If your heart is pure, it does not matter whether you perform namâz, drink alcoholic beverages, or go out naked.” What do you advise me to write her in reply?
We advise you not to write anything at all because it is stated, “The best answer to an idiot is silence.” Every work has a doer. Is there idiocy worse than saying the moon, sun, stars, planets, plants, animals and humans have come into being (without a creator) by chance? 

If we set forth what is true, good and nice for the atheist, does it provide any benefit? It does not at all. The reason it is so because it is declared in the Qur’ân al-karîm clearly that they cannot hear what is right, see the truth and say the facts. It is purported in an âyat-i karîma:
(Since disbelievers are deaf, dumb and blind, they cannot reason.) [Sûrat-ul-Baqara, 171]

That is, since they do not hear what is right, they are deaf; since they do not say the truth, they are dumb; and since they do not see the facts, they are blind. (Baydâwî)

Religionist is someone who engages in religion trade, who buys and sells religion. As for those who observe the rules of Islam, they are called Muslims. She who performs namâz and covers herself is a Muslim, not a religionist or an extremist. Atheists do not insult Muslims by using the term Muslim, but by labelling them as religionists or extremists. If we ask them what a religionist is, they define a Muslim. In other words, they say, “A religionist performs namâz, observes fast, and does not drink alcoholic beverages.” (Taking into account this definition) since a religionist is a Muslim, why does the atheist not attack by saying obviously that being a Muslim is bad, but by saying that being a religionist is bad? If, in atheist’s opinion, a religionist is someone who performs the commandments of Islam and avoids its prohibitions, why then is she criticizing you by saying “extremist”? In this case, logically, an extremist would be someone who adheres more strictly to the commandments of Islam. If the religion is good, then being a religionist, too, is good; in this sense, being a strict religionist is better. If the religion is bad, then being a religionist, too, is bad; in this sense, being a strict religionist is worse. This means to say that they use the word “extremist” to denigrate being a Muslim. A Muslim, in their mind, is someone who does not carry out any commandments and does not abstain from any prohibitions.

Allahu ta’âlâ, Who has created everything from nothing, and His Messenger stated how the heart becomes purified: The hearts of those who live up to what Allah and His Messenger communicated are pure, while the hearts of those who do not obey their commandments are foul. Committing sins is a symptom of a heart’s being corrupt. For this reason, it is out of place for those who commit such sins as not performing namâz or going out by not covering oneself to say, “You should look at my heart. It is pure.” As a matter of fact, the Messenger of Allah declares:
(When a person commits a sin, a black spot forms in his heart. If he makes repentance, that spot is removed. But if he does not make repentance and commits a yet another sin, that spot enlarges and covers his heart. Then his heart becomes pitch-black [dirty, foul].[Haraitî]

(The heart of a person who continues committing sins is sealed. Therefore, he can no longer do a thawâb-deserving deed.)[Bazzâr]

(If the heart is corrupt, the deeds of the body are, invariably, corrupt, too.) [Bayhaqî]

The heart mentioned herein is the heart of person who does not avoid harâms though being a Muslim. The purport of a hadîth-i sharîf is as follows:
(A Believer’s heart is pure; a disbeliever’s heart is pitch- black.)[Tabarânî]