(Certainly those who say, "Allah is the third of three" have disbelieved)

This is a commencement to clarify the disbelief of a group among them, and it has already been explained to you who they are. "The third of three" (thālithu thalāthah) cannot be anything but genitive (iḍāfah), as al-Farrā’ stated, and likewise "the fourth of four" and similar structures; the meaning of this is that He is one of those numbers, not that He is the third or fourth specifically. If you were to say, "the third of two" or "the fourth of three," for example, both are permissible: the genitive (iḍāfah) and the accusative (naṣb). Al-Zajjāj has also explicitly stated this.

They intended by the "three," according to what is narrated from al-Suddī: the Creator (Mighty and Majestic is His Name), ‘Īsā, and his mother (peace be upon them both). Thus, according to their claim, each of the three is a god, and divinity is shared between them. This is corroborated by the Almighty’s saying to the Messiah (peace be upon him): "Did you say to the people, 'Take me and my mother as two gods besides Allah?'" This is what is suggested by the literal meaning of the Almighty’s saying: (And there is no god except One God)—meaning, while it is the case that among existing things, there is no Necessary Being worthy of worship, for He is the origin of all existing things, except a God characterized by Oneness, exalted above accepting association in any way; since multiplicity necessitates the negation of divinity, as the proof of mutual antagonism (burhān al-tamānu‘) indicates. So if absolute multiplicity contradicts divinity, what then of the Trinity?

The min (in "min ilāh") is extra, for the purpose of generalization (istighrāq), as the grammarians have explicitly stated. They explained its rationale by saying that it is originally from the min of commencement (al-ibtidā’iyyah), where its counterpart is omitted to indicate infinitude. Thus, the origin of "there is no man" (lā min rajul) is "there is not from a man to what has no end." This is the essence of what the author of al-Iqlīd mentioned regarding this.

It is said that they say: Allah (Glory be to Him) is one substance with three hypostases (aqānīm): the hypostasis of the Father, the hypostasis of the Son, and the hypostasis of the Holy Spirit. By the first, they mean the Essence; it is also said they mean Existence, by the second Knowledge, and by the third Life. Some of them have spoken of their incarnation. Therefore, the meaning of the Almighty’s saying: (And there is no god except One God) is: There is no god by essence, who is transcendent above the blemish of multiplicity in any of the ways they claim. The verification of this position has already passed with a level of detail that cannot be exceeded, so refer back to it if you desire.

(And if they do not desist from what they are saying)—that is, if they do not return from what they are upon to its opposite, which is Tawḥīd and faith—(a painful punishment shall surely afflict those who disbelieved among them).

This is a response to an omitted oath that has taken the place of the conditional response (jawāb al-sharṭ), according to what Abū al-Baqā’ said. The intended meaning of "those who disbelieved" is either those who remain firm in disbelief, as chosen by al-Jubbā’ī and al-Zajjāj, or the Christians, as has been said. The relative pronoun (al-ladhīna) was placed in the position of their pronoun to repeat the testimony against them of disbelief. Min (in "minhum") is explanatory (bayāniyyah) based on the latter view, and partitive (tab‘īḍiyyah) based on the former. The verb that indicates occurrence (li-yamassanna) was used to alert that continuing upon it after what has arrived—which necessitates desisting from it—is a new disbelief and an excess of transgression beyond what they were upon originally in their disbelief.