For the Son of God, Jesus Christ, who was preached among you by us, even by me and Silas and Timothy, was not yea and nay, but in him was yea.
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Competent preachers ought to be unambiguous about what they say. Say nothing that is not beneficial. Given that our human will often tends in ambivalent directions, Paul is insistent that he is not acting according to his will but according to what he knows will be helpful. In Christ, of course, this problem does not exist, because he always wills what is beneficial. Furthermore, Christ’s will never changes and is never uncertain. Commentary on Paul’s Epistles.
And when we confess that we have lied, we speak the truth, for we are saying what we know, and we know that we have lied. That Word, however, which is God and more powerful than ourselves, cannot do this… . And of himself he does not speak, but of that Father is everything that he speaks, since the Father speaks it in a unique way. The great power of that Word is that he cannot lie, because in him there cannot be yes and no but yes, yes; no, no. For that is not even to be called a word if it is not true.
For the Son of God . . . was not yea and nay, but in Him was yea. My preaching and teaching about Christ was not variable, inconstant, and contradictory, but was a constant, uniform statement, for I always said and taught the same of Christ.
It is, was in him. There was no inconstancy in the doctrine of the apostles, sometimes, like modern sectaries, saying, It is, and at other times saying, It is not. But their doctrine was ever the same, one uniform yea, in Jesus Christ, one Amen, that is, one truth in him. (Challoner)
For on this account he brings before them the company of the teachers also, as thence too giving credibility to the testimony by those who taught, and not who heard it only. And yet they were disciples; however in his modesty he counts them as in the rank of teachers. But what is, was not yea and nay? I have never, he says, unsaid what before I said in the Preaching. My discourse to you was not now this, now that. For this is not of faith, but of an erring mind.
But in Him was the yea. That is, just as I said, the word abides unshaken and steadfast.