As for your statement that Christians may allude to the doctrine of the Kullābiyya, the answer is that if Christian doctrine consisted solely in affirming that Allah is living by virtue of life and knowing by virtue of knowledge, then their doctrine, yours, and that of the Kullābiyya would be the same.
Allah did not declare Christians unbelievers on this account. Rather, He declared them unbelievers because of what He related about them in His Book—beliefs held by none of the Muslim affirmers of the attributes. Christian doctrine contains contradictions and inconsistencies whose unsoundness is evident to every rational person: they affirm the Son as an attribute—a hypostasis—yet also make him a god who acts, while nevertheless asserting that God is one. They say that the one united with Christ is the Son, who is the Word, not the Father. Their doctrine is thus contradictory, like that of the philosophers. Indeed, the Muʿtazila are also contradictory in their denial and affirmation of the attributes, as you can see. These are the words of the most distinguished of their later scholars.
He advanced only two arguments against the affirmers of the attributes. The first is that if Allah possessed knowledge, His knowledge would be like ours, and of two things alike, one cannot have come into existence while the other is beginningless.
The second is that His being knowing and powerful is necessary, and that when an attribute is necessary, its necessity makes it independent of any underlying quality that would necessitate it. He has thus called this an attribute. This argument, however, applies only to those who affirm states, and they maintain that something necessary can be explained by something else that is necessary.
As for the first argument, its unsoundness is abundantly clear, especially since Abū al-Husayn does not concede to them that any of us is knowing by virtue of an underlying quality. Hence, he abandoned his teachers’ two aforementioned approaches to denying the attributes in favour of a third, weaker than either, saying that there is no way to establish these underlying qualities