"You shall not muzzle an ox when it is treading out the grain.
This might seem like a strange law to include within the scriptures, but once again we can see the deep wisdom of God at work if we take the time to understand his purpose in the law.
The reason why an ox is unmuzzled is so that it can eat while it works. The way a farmer, who wanted to take in as much harvest as possible, would use his ox is to muzzle it so that it could not eat the grain. God wants the ox to be able to eat the grain so that it can sustain itself while it serves it's master. And not only that, it can eat as much or as little as it needs.
It doesn't stop there. In other parts of the bible, the ox is likened to pastor/teachers of God's people. The grain is the income (as food, products, or money) which the people who are served by the teacher earn. God wants those who serve his people in ministry to earn their living by receiving a part of the "grain" from his people. As much or as little that they need, they should receive from the people of God.
This is also a practical consideration because the teacher will be sacrificing his ability to work a normal job to earn a living. It makes sense that he be supported by those who benefit from his teaching.