The "People of the Book" in Islamic law are the Jews and the Christians (later in history, that was generously expanded to include Hindus).
Muslims like to tell us, slyly, that The "People of the Book" were treated well and were "protected" under Islamic law.
Koran 5:17, however, makes it clear that Christians were also categorized as Kuffar (a plural form of Kafir):
The original Arabic leaves no doubt: the word used is kafara (a simple declension in the plural of Kafir); and see also 5:73, where the Trinity is explicitly condemned in terms of kafara.
In this regard, 9:30 establishes that both Jews and Christians are disbelievers (kafaroo) by virtue of committing the cardinal sin of Shirk for which, under Islamic law, the penalty is death:
And the Jews say: Ezra is the son of Allah, and the Christians say: The
Messiah is the son of Allah. That is their saying with their mouths.
They imitate the saying of those who disbelieved of old. Allah (Himself)
fighteth against them. How perverse are they!
And about the Jews being Kuffar, see also Koran 2:89:
When there came to them a Book from God, confirming what was with them --
and they aforetimes prayed for victory over the unbelievers -- when
there came to them that they recognized, they disbelieved in it; and the
curse of God is on the unbelievers.
2:89 is furthermore ironic, in that it is saying that this particular People of the Book were Kuffar (they "disbelieved" -- kafaroo) in relation to the Book! (The "Book" in this case being the eternal guidance of Allah, in the form of the Taurat (Torah) which, however, the wicked Jews, according to Islam, forthwith twisted and corrupted.)
2:89 is furthermore ironic, in that it is saying that this particular People of the Book were Kuffar (they "disbelieved" -- kafaroo) in relation to the Book! (The "Book" in this case being the eternal guidance of Allah, in the form of the Taurat (Torah) which, however, the wicked Jews, according to Islam, forthwith twisted and corrupted.)
This is of critical importance because logically it means that all the hateful and violent things that apply to Kuffar in the Koran (and Hadiths) also apply to Christians and Jews -- despite what slyly deceitful Muslims might otherwise claim when taqiyya-spinning.
Thus, as we have seen above, Kufr (the conceptual noun form -- "Disbelief") is intimately bound up with Shirk (compromising the monotheism of Allah by "associating partners" with him). And for those who practice Shirk (the Mushrikoon), Koran 9:28 makes clear that Allah hates them and fights and kills them (obviously through the agency of his loyal Muslim followers). And 9:28 is also the verse infamous for calling such miscreants as the Mushrikoon "filthy" (najasun).
Conclusion:
If Muslims think of the People of the Book as no better than worms, to be crushed under foot if they do not, as virtual slaves, pay the jizya willingly and feel humiliated in doing so, as no more than silkworms bred and maintained for nothing else than their labor and the fruit thereof (as well as to be abused for the pleasure of Muslims like children tormenting an insect with a stick); we can say that Christians and Jews, as autodidacts in this incrementally progressive (if still at a snail's pace) War of Ideas, are slowly but surely becoming bookworms about that book at the diseased heart of that religion destined someday (let us hope at least within this century, for Allah's sake!) to be food for worms.
