1 Corinthians 9:10 (ESV)

10 Does he not certainly speak for our sake? It was written for our sake, because the plowman should plow in hope and the thresher thresh in hope of sharing in the crop.

Paul reminds the Corinthians of a well-established rule for interpreting Scripture (see, e.g., Romans 15:4; 2 Timothy 3:16–17). The common acceptance of this rule is probably what is indicated by the word certainly (which can also be translated as no doubt).

This rule is that all of Scripture is intended specifically for the covenant people of God. Everything, even laws concerning oxen, is written for the benefit of believers. The law in Deuteronomy 25:4, then, has been given primarily so that human workers may work in hope of enjoying the fruit of their labour.