1 Corinthians 9:14
Even so hath the Lord ordained that they which preach the gospel should live of the gospel.
Note 11 at 1Co 9:14: Paul was probably referring to the words of the Lord Jesus found in Mt 10:9-10 and Lu 10:7. "And in the same house remain, eating and drinking such things as they give: for the labourer is worthy of his hire" (Lu 10:7).
Note 12 at 1Co 9:14: This was not man's idea. The Lord is the one who instituted the practice of ministers having their needs met by those to whom they minister. The Lord could have arranged for ministers' needs to be met some other way, but there are reasons for doing it this way. One of the most important reasons is that this way, those who support the Gospel get to partake of all the rewards that come to the minister (1Sa 30:24-25). They become partners (Ro 10:14-15). Paul told the Philippians that he desired a gift from them because he wanted them to have "fruit that may abound to [their] account" (Php 4:17, brackets mine). Therefore, the people receiving ministry would miss a huge blessing if the Lord supplied ministers' needs some other way. Also, this provides another incentive for ministers to do a good job. If ministers aren't ministering very much or very well, their finances dry up. This should not be the primary motivation for being a good minister, but it certainly is one that every minister can understand.
Note 13 at 1Co 9:14: Not only should ministers' livelihoods come from preaching the Gospel, but it should also be proportional to their preaching of the Gospel. Those who spend very little time ministering the Gospel should expect to receive very little of their income from the Gospel. When ministers are totally occupied with ministering the Gospel, they can expect to live full time off the Gospel. It is not wrong for ministers who are just getting started and have few opportunities to minister, to supplement their income with secular work. Instead, it is far superior for them to work for a time and have their needs met than to suffer the hardships that come from being without money. Ministers do not have to receive all their income from preaching the Gospel to be committed to their calling.