John Chrysostom, on 1Cor 9:7

"What soldier ever serveth at his own charges?"

For since, which was the strongest point, he had proved from the Apostles that it is lawful to do so, he next comes to examples and to the common practice; as he uses to do: "What soldier serveth at his own charges?" saith he. But do thou consider, I pray, how very suitable are the examples to his proposed subject, and how he mentions first that which is accompanied with danger; viz. soldiership and arms and wars. For such a kind of thing was the Apostolate, nay rather much more hazardous than these. For not with men alone was their warfare, but with demons also, and against the prince of those beings was their battle array. What he saith therefore is this: "Not even do heathen governors, cruel and unjust as they are, require their soldiers to endure service and peril and live on their own means. How then could Christ ever have required this?"

Nor is he satisfied with one example. For to him who is rather simple and dull, this also is wont to come as a great refreshment, viz. their seeing the common custom also going along with the laws of God. Wherefore he proceeds to another topic also and says, "Who planteth a vineyard, and eateth not of the fruit thereof?" For as by the former he indicated his dangers, so by this his labor and abundant travail and care.

He adds likewise a third example, saying, "Who feedeth a flock, and eateth not of the milk thereof?" He is exhibiting the great concern which it becomes a teacher to show for those who are under his rule. For, in fact, the Apostles were both soldiers and husbandmen and shepherds, not of the earth nor of irrational animals, nor in such wars as are perceptible by sense; but of reasonable souls and in battle array with the demons.

It also must be remarked how every where he preserves moderation, seeking the useful only, not the extraordinary. For he said not, "What soldier serveth and is not enriched?" but, "What soldier ever serveth at his own charges?" Neither did he say, "Who planteth a vineyard, and gathereth not gold, or spareth to collect the whole fruit?" but, "Who eateth not of the fruit thereof?" Neither did he say, "Who feedeth a flock, and maketh not merchandize of the lambs?" But what? "And eateth not of the milk thereof?" Not of the lambs, but of the milk; signifying, that a little relief should be enough for the teacher, even his necessary food alone. (This refers to those who would devour all and gather the whole of the fruit.) "So likewise the Lord ordained," saying, "The laborer is worthy of his food."

And not this only doth he establish by his illustrations, but he shows also what kind of man a priest ought to be. For he ought to possess both the courage of a soldier and the diligence of a husbandman and the carefulness of a shepherd, and after all these, to seek nothing more than necessaries.