John Calvin Commentary Titus 3:14

"And let our [people] also learn to maintain good works for necessary uses, that they be not unfruitful." — Titus 3:14 (ASV)

And let ours also learn to excel in good works. So that the Cretans, on whom he places this burden, might not complain of being burdened with the expense, he reminds them that they must not be unfruitful, and that they must therefore be earnestly exhorted to be zealous in good works.

However, we have already spoken of this mode of expression. Therefore, whether he commands them to excel in good works or to assign the highest importance to good works, he means that it is useful for them to have an opportunity provided for exercising generosity. This is so they might not be “unfruitful” because there is no opportunity, or because necessity does not demand it.

What follows has already been explained in the other Epistles.