Sanctity of a Muslim

On the authority of the son of 'Umar (radi Allaahu 'anhumaa) that the Messenger of Allaah (sallAllaahu alayhi wa sallam) said:

I have been ordered to fight against the people until they testify that there is none worthy of Worship except Allaah and that Muhammad is the Messenger of Allaah, and until they establish the Salaah and pay the Zakaah. And if they do that then they will have gained protection from me for their lives and property, unless [they commit acts that are punishable] in Islaam, and their Reckoning will be with Allaah. [Related by Bukhaaree and Muslim]

Explanation of Hadeeth 8
This is a Great Hadeeth and a Principle from amongst the Principles of the Religion. It has also been narrated by Anas (radi Allaahu 'anhu) whose version mentions:

"Until they testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger, and accept our Qiblah, and eat from what we slaughter, and and pray our Salaah. And if they do all that, then their blood and wealth is Protected except from the Rights of Islaam. And for them is what is for the Muslims and upon them is what is upon the Muslims."
And it has come in Saheeh Muslim from the narration of Abu Hurayrah (radiAllaahu 'anhu):

"Until they testify that there is none worthy of worship except Allaah and believe in me and in what I have come with"
and this has the same meaning as what Ibn 'Umar narrated.

As for the meaning of this hadeeth, then the scholars of seerah have said:

After the death of the Prophet sallAllaahu alayhi wa sallam, Abu Bakr as-Siddeeq radiAllaahu 'anhu became the Khaleefah, and some of the Arab tribes apostasized, so Abu Bakr prepared to fight them. And amongst them were those who refused to pay the Zakaah, but who had not explicitly apostasized. So 'Umar radiAllaahu 'anhu said to Abu Bakr:
"How can you fight a people who have said 'laa ilaaha illaa Allaah' and the Prophet sallAllaahu alayhi wa sallam said 'I have been ordered to fight the people until they say 'laa ilaaha illaa Allaah'?" So Abu Bakr radiAllaahu 'anhu replied : "By Allaah! If they refuse to pay (in Zakaah) a young goat that they used to pay the Prophet sallAllaahu alayhi wa sallam, I will fight them."

And 'Umar radiAllaahu 'anhu followed him in doing this.

Regarding the statement of the Prophet sallAllaahu alayhi wa salaam "I have been ordered to fight the people until they say 'laa ilaahaa illaa Allaah' ..." al-Khattaabee rahimahu Allaah and others said:

The people referred to here are the idol worshippers and the mushriks of the Arabs, and those who do not believe apart from the People of the Book. And whoever approves of Tawheed from his own religion of Kufr, then his statement of 'laa ilaaha illaa Allaah' is not enough to protect his blood and wealth, as has come in other narrations that mention that one must also believe that Muhammad is the Messenger of Allaah, and establish the Salaah, and pay the Zakaah.
And Shaykh Muyee ad-Deen an-Nawawee said:

"And it is necessary that he believes along with this in all that the Messenger sallAllaahu alayhi wa sallam came with, as is mentioned in the hadeeth of Abu Hurayrah : 'until they testify that none is worthy of worship except Allaah, and believe in me and in all that I come with'".
And the meaning of his (sallAllaahu alayhi wa sallam) statement: "and their Reckoning will be with Allaah" refers to those matters which they hide from the people, i.e. those things other than that which is outwardly apparent from the compulsory actions. Al-Khattaabee mentions this and then says:

"And from this is that the one who outwardly shows Islaam but secretly maintains Kufr, then his Islaam is accepted outwardly by the people, and this is the opinion of most of the People of Knowledge."
And in his (sallAllaahu alayi wa sallam) statement: "I have been ordered to fight the people until they testify that none is worthy of worship except Allaah, and believe in me and in all that I come with" is a clear proof for the position of the People of Truth and the vast majority of the Salaf and the Khalaf, that it is enough for a person to believe in the Religion of Islaam with a firm, unwavering belief, without it being necessary for him to understand the proofs of the Mutakallimoon (people of Theological Rhetoric) regarding the 'recognition' of Allaah through the intellect. And this opposite to the statement of those people that it is an obligatory condition for the correctness of ones eemaan. And this is clear from the fact the Prophet sallAllaahu alayhi wa sallam mentioned only at-Tasdeeq (belief, affirmation) and did not lay any condition for it through intellectual recognition. And this hadeeth appears a number of times in the Saheeh, and together they reach the rank of mutawaatir, without doubt yielding definite knowledge, and Allaah knows best.

Summary
That the disbelieving people are fought until Islaam triumphs.
That it is an order from Allaah and thus waajib.
That the Ameer of the Muslims enforces protection of the lives and the properties of the Muslims.
That if a Muslim does something which deserves a punishment according to the Rulings of Islaam, then the Ameer of the Muslims must enforce that too.
That the punishments must be given, regardless of what Allaah will Judge for them (i.e. Allaah may punish them or forgive them).