What does 1 Timothy 5:18 mean?

In Paul's writings, reference to "Scripture" almost always means the Old Testament. The first quote regarding an ox and grain is from Deuteronomy 25:4, the final book of the Torah. This verse has both a specific and general application. Putting a muzzle on the ox would prevent it from eating grain while it was working. This might save a small amount of grain, but it means the ox can't replenish its strength while it works.

It is more sensible—and fair—to let the animal eat while it works. The net benefit is considerable. In the more general sense, as Paul is using it here, this also means it's both beneficial and fair for those who labor in teaching and preaching in the church to be paid for their work. This is primarily so they can devote their time and energy fully to service of the congregation.

Interestingly, the second quote is from Jesus. These words appear in Luke 10:7 and are similar to Matthew 10:10. Note that Paul is referring to both quotations as "Scripture," meaning Paul is placing Luke's writing in the same category as the Old Testament: inspired Scripture. This strongly supports the notion that the apostles knew they were writing divinely-inspired words.

Also, this quotation shows the Gospel of Luke had almost certainly been written by this time. This would date the Gospel of Luke after AD 62, which was the end of Paul's house arrest in Rome,. It would also date the Gospel of Luke prior to the time 1 Timothy was written, which was approximately AD 64.

The actual quote, "The laborer deserves his wages" reinforces Paul's teaching that elders who work hard are to be paid for their efforts (1 Timothy 5:17).