1 Corinthians 15:15

And what in this case are the apostles who have borne witness to the world of an unreal fact? Impostors, and impostors of the worst kind, for their testimony bears on a false fact which they dared to ascribe to God Himself! The verb εὑρισκόμεθα, we are found, expresses the idea of surprisal: “Lo, we are taken in the flagrant sin of falsehood!” The word ψευδομάρτυρες θεοῦ, false witnesses of God, might be understood in the sense: “Divine messengers giving false testimony;” the gen. θεοῦ being made dependent on μάρτυρες alone. Or it might be explained in the sense: “Falsely calling ourselves messengers of God;” θεοῦ depending in this case on the term ψευδομάρτυρες taken as a whole. But the explanation which best agrees with the context is this: “Testifying falsely in regard to God;” in the sense that, as is said afterwards, the apostles ascribe to God a work which He never really did. The gen. θεοῦ is that of the object: false witnesses regarding God, and even according to the following words: κατὰ τοῦ θεοῦ, against God. Such a testimony is indeed an act of impiety, an act of violence to God Himself. For is it not to assail His honour to ascribe an act to Him which He never really did? It is exactly the same as if an act done by Him were denied.

The conj. εἴπερ, if truly, recalls the saying of the τίνες : “If the thing is real, as they allege.”