1 Timothy 5:18
For the scripture saith, Thou shalt not muzzle the ox that treadeth out the corn. And, The labourer [is] worthy of his reward.
Note 6 at 1Ti 5:18: In 1Ti 5:17, Paul instructed Timothy to give the elders who were doing a good job twice the financial benefits as the other elders, especially those who labored in the Word and in doctrine. Here, he drew on Scripture to reinforce his instructions.
De 25:4 commands us not to muzzle the oxen that tread out the corn. In 1Co 9:9-10, Paul used this same scripture and made it clear that this was written for the purpose of teaching about ministers receiving money, not about how to feed oxen.
The illustration is that in the same way an ox that is working needs to be fed, a minister who is ministering, needs to have his needs met too. Many people would treat their barnyard animals better than their ministers, if not instructed otherwise.
Note 7 at 1Ti 5:18: Paul used an Old Testament scripture from De 25:4 to verify his instructions about ministers receiving financial benefits from those to whom they minister (see note 6 at this verse). Here, he quoted Jesus on this same issue and referred to what Jesus said as the Word of God. He referred to Jesus' statement to the disciples He had sent out. He told them not to provide money for themselves and not to go from house to house as beggars, because "the labourer is worthy of his hire" (Lu 10:7).
Jesus was teaching that ministers deserve the support of those to whom they minister. They shouldn't look at others' support as pity but as payment. Those who labor at secular jobs don't look at their paychecks as charity; they earned their pay. Many people see ministers as just living off of other people, but if they are godly ministers, that is not so. They are laboring in the Word and doctrine, which is very important and deserving of a good paycheck.