1Thess 2:10

“On this account he frequently addresses them as witnesses. For "ye are witnesses," he says, "and God also"; God was worthy to be believed, but this other was that which most fully assured them. For that indeed was uncertain to those who were ignorant of it; but this was without doubt to all. For do not enquire whether it was Paul who said these things. Much beyond what was necessary he gives them assurance. Wherefore he says, "Ye are witnesses, and God also, how holily and righteously and unblamably we behaved ourselves toward you that believe." It was proper to praise them again. On this account he sets these things before them, which were sufficient to persuade them. For he that stood there in want, and did not receive anything, would much more not receive anything now. "How holily," says he, "and righteously and unblamably we behaved ourselves toward you that believe."”

“God is a trustworthy witness, but since people do not know whether God testifies to this, he also calls as witnesses those to whom the word is addressed. Fulfilling all that is required, for this is the meaning of "holy," in place of the expression: with the fear of God. That is, not extorting money from anyone – demanding exactions of money. Not offending and not giving occasion for stumbling. Then whereas among the unbelievers the apostle was called godless and a deceiver, a babbler and utterly senseless.”

“Then when Paul says: you are witnesses, he remarks on the orthodoxy of his discourse. First, he speaks about the sanctifying influence it may have on a person's life; secondly, he shows how full of concern his teaching was (2:11). So Paul remarks: you are witnesses how holy, that is, how innocently, we conducted ourselves: "Be holy, for I am holy" (Lev. 11:44 and 19:2); and righteous toward our neighbor, as is made evident by "to live sober, upright and godly lives in this world" (Tit. 2:12); and blameless was our behaviour to you believers, which means that you believed because we have done nothing that could have caused anyone to be scandalized. To you believers, individually. It should be noted that sometimes a singular predication has considerable import.”