Paul had seen the Lord in glory and could insist on his apostleship. He may have been meek and lowly and dependent, to fight against Satan, but he insisted upon his authority as an apostle. The Corinthian saints were a proof of His apostleship. He says, "Am I not free" to marry, to cease working?
Sowing spiritual things should call for a return in carnal things, such as food, clothing, a bed, and essentials. The ones who preach the gospel should be supported.
The apostle was called by the Lord and was bound to preach the gospel, but he would not take support from Corinth, lest he hinder the work that was on his heart. He made tents to pay expenses.
Paul desired to bring salvation to man and bowed himself in the dust to do it.
Those who strive for mastery should be temperate in all things in view of an incorruptible crown. It will not do to beat the air, but before God we keep our bodies under, not allowing the flesh to act, lest one should be a castaway-lost.