9 But there is another more recondite meaning in these words which it is not difficult to understand, which respects more particularly myself and all dispensers, and you too who are hearers. He that salutes, wishes salvation. For so the ancients in their letters wrote thus, “Such a one sends salvation to another.” Salutation derives its name from this salvation. What then is, “Salute no man by the way”? They who “salute by the way,” do so “by occasion.” I see that you have quickly understood me, yet for all that I must not finish yet.
For you have not all understood so quickly. I have seen that some understand by their voice, I see more asking for something further by their silence. But seeing that we are talking of the way, let us walk as it were in the way: ye quick ones, wait for the slow, and walk evenly. What then did I say, He “who salutes by the way,” salutes only by occasion? He was not going to him whom he salutes. He was about one thing, another came in his way; he was seeking one thing, he found across his path some other thing to do.
What then is it to “salute by occasion”? “By occasion” to announce salvation. Now what else is it to announce salvation, but to preach the Gospel? If then you preach, do it by love, and not “by occasion.” There are men then, who though “they seek their own things,” yet preach no other Gospel; of whom the Apostle says with sighing, “For all seek their own, not the things which are Jesus Christ's.” And these “saluted,” that is announced salvation, they preached the Gospel; but they sought some other thing, and therefore they saluted only “by occasion.” And what is this? If you are such an one, whosoever you are, you do it; nay not all of you who do it are such, but it may be that some of you who do it are. But if you are such, it is not that you do it, but it is done by you.
Source: Sermons on Selected Lessons of the New Testament (New Advent)