Apparently the Corinthians are examining Paul's apostolic authority (also 2:14-15, 4:3).
(a) Paul has "freedom" or "right" to eat certain food, although he is willing to give it up (8:13).
(b) Paul has the "right" to be married but did not exercise it.
(c) Paul has the "right" to get their material support and not work for his living.
The soldider, farmer, and shepherd all expect to be sustained from his work. Similarly, Paul should expect to be sustained from his "flock"--the church that owes its existence to him.
Paul explains that his reasoning is founded not only to human perspective but on the Scripture.
The Israelites were forbidden to muzzle the ox, out of mercy for the labouring animal (Dt 25:4).
"Spiritual seed" is more precious in contrast to "material harvest".
All previous examples are indirect analogies; the analogy of the temple workers (both Jewish and pagan) here is a direct analogy.
The teaching is supported by Christ in Lk 10:7 ("the worker deserves his wages") which was spoken in the context of his sending out the 72 disciples.
Paul's boast is not that he preaches the gospel. His compulsion is not an "inner compulsion"; it is a desire and a necessity to do what was designed and appointed by God.
One might perform the task voluntarily as a free person or involuntarily as a slave. If one is free and does it voluntarily, then one is entitled to "pay" or a "reward". If his labour is involuntary (like that of Paul in v.16), then he is not entitled to pay.
Paul's reward (and his boast) for not accepting material support is his apostolic "freedom" so that: (a) he can make the "free" gospel "free of charge" so that he will not "misuse" his "rights" or "freedom" (material support from them); (b) he might be more freely make himself a slave to everyone (v.19); (c) he has total freedom from all merely human impositions on his ministry and no one except Christ has a claim on him (v.19).
Paul has paradoxically used his freedom to become "a slave to everyone"--to serve everyone. This is surely the ultimate expression of truly Christian and Christlike behaviour.
Paul tries to accommodate himself to whatever social setting he found himself in.
To assure the Corinthians that "not having (or under) the law" (v.20) does not mean "lawless", Paul confirms that he is under God's law.
"The weak" likely refers to those with weak conscience in 8:7-13.
Paul's behaviour was all "for the sake of (the progress) of the gospel"--to "win" (v.19-22) or "save" (v.22) someone. The "blessings" and the "crown" (v.25) is interpreted variously as eternal life, spiritual growth, or reward from God. In view of such blessings, Paul exhorts them to "run in such a way as to get the prize" (v.24) and not be "disqualified" (v.27).
In ministry, there is no real competition among Christians, but the attitude should be one of urgency as if there is only one prize.
In order to win the prize, runners must exercise self-control and self-discipline. The Corinthians' lack of self-control is in their insistence on the right to eat pagan feasts.
Runners compete for a perishable prize; believers for the imperishable one.
The examples of runners and boxers are illustrations of purposefulness. For these people, the acts of running aimlessly and boxing the air are simply absurd and senseless.
We are to make our lives serve our purposes in the gospel. Without self-control (such as the Corinthians' insistence on attending pagan feasts), one can fail to obtain the prize.
If the prize refers to eternal life, then can someone lose it? It is not clear in this letter as Paul always keeps both warning and assurance of salvation in tension (6:9-11, 10:11-13).