30 Moreover, it was said to the Apostles that they should take nothing with them for their journey, but should live by the Gospel. And in a certain place too the Lord Himself signified why He said this, when He added, “The laborer is worthy of his hire:” where He sufficiently shows that this is permitted, not ordered; lest haply he who should do this, namely, that in this work of preaching the word he should take anything for the uses of this life from them to whom he preached, should think he was doing any thing unlawful. And yet that it may more laudably not be done is sufficiently proved in the Apostle Paul: who, while he said, “Let him that is taught in the word, communicate unto him, that teaches in all things,” and showed in many places that this is wholesomely done by them to whom he preached the word, “Nevertheless,” says he, “I have not used this power.” The Lord, therefore, when He spoke those words, gave power, not bound men by a command. So in general, what in words we are not able to understand, in the actions of the Saints we gather how it is meet to be taken, which would easily be drawn to the other side, unless it were recalled by an example.
Source: On Lying (New Advent)