10 For such as these did the Apostle suffer; yet did he not enjoin them so to be. And these do something, or something is done by them; they seek something else, yet they preach the word. Care not what the preacher seeks after; be it your will to hold fast what he preaches; but let his intention be no concern of yours. Hear the word of salvation from his mouth, from his mouth hold fast this salvation. Be not the judge of his heart. If you see that he is seeking after other things, what is that to you?
Hear Him who is Salvation; “What they say, do.” He has given you assurance who has said, “What they say, do.” Do they evil? “Do not what they do.” Do they good. They do not “salute by the way,” they do not preach the Gospel by occasion; “be ye followers of them, even as they also are of Christ.” A good man preaches to you; pluck the grape from the vine. A bad man preaches to you, pluck the grape as it hangs in the hedge. The cluster has grown on the vine-branch entangled among the thorns, but it has not grown from the thorns.
By all means when you see any such thing as this and art hungry, be careful as you pluck it, lest when you put forth your hand to the grape, you be torn by the thorns. This is what I say; in such wise hear what is good, as that you imitate not the evil of the character. Let him preach “by occasion,” salute by the way; it will injure him because he has not given ear to the precept of Christ, “Salute no man by the way;” it will not injure you, who, whether you hear of salvation from a passer by, or from one who comes direct to you, dost hold fast that salvation.
Hear the Apostle, who as I have said already gives us to understand this. “What then?” “So that in every way, whether by occasion or in truth, Christ is preached; and herein I do rejoice, yea, and will rejoice. For I know that this shall turn to my salvation through your prayer.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)