Is one still a Muslim when he consciously disobeys a "law"?

Question

In the Quran much is written about what is wrong and what is right.

If a Muslim knows that something is wrong, and still does it (or that something is right and doesn't do it) - is he still considered a Muslim, or how strict does it get? What does the Quran say about it? What are the consequences?

Please try to get as much cites in your answer as possible! Thank you indeed!

I ask this question as for example in 5:51 it is written that one who takes Christians and Jews as allies (or friends) is one of them - and therefore not a Muslim anymore. And I wondered... wow this is pretty strict. But I don't want to hear "no it's not that strict, don't take it that seriously" but the truth! How strict does it get and what does the Quran say about "just living the life" and just claiming to be a Muslim but not really caring what the Quran really says... or disobeying some things the Quran tells.

Answer 1

In general, disobeying a law of Islam is not Kufr in itself. The evidence for this includes:

إن تستغفر لهم سبعين مرة فلن يغفر الله لهم ذلك بأنهم كفروا بالله ورسوله

If you should ask forgiveness for them seventy times - never will Allah forgive them. That is because they disbelieved in Allah and His Messenger.

^{— Quran 9:80}

إن الله لا يغفر أن يشرك به ويغفر ما دون ذلك لمن يشاء ومن يشرك بالله فقد افترى إثما عظيما

Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills. And he who associates others with Allah has certainly fabricated a tremendous sin.

^{— Quran 4:48}

Here Allah tells us that He might forgive any sin that is less than Kufr and Shirk, which proves that there exist sins that are not Kufr and Shirk. Since those sins are not Kufr, doing them does not make one a non-Muslim.

However disobeying some laws does make one a non-Muslim. This includes doing any action which explicitly implies disbelief or is the distinctive behavior of disbelievers. For example: uttering a statement professing disbelief in or disassociation from any agreed-upon teaching of Islam, prostrating towards an idol, insulting a Messenger, disrespecting a copy of the Quran, allying with non-Muslims in a war against the Muslims etc.