14 In the same way, the Lord has commanded that those who preach the gospel should receive their living from the gospel. 15 But I have not used any of these rights. And I am not writing this in the hope that you will do such things for me, for I would rather die than allow anyone to deprive me of this boast. 16 For when I preach the gospel, I cannot boast, since I am compelled to preach. Woe to me if I do not preach the gospel! 17 If I preach voluntarily, I have a reward; if not voluntarily, I am simply discharging the trust committed to me. 18 What then is my reward? Just this: that in preaching the gospel I may offer it free of charge, and so not make full use of my rights as a preacher of the gospel.—1 Cor. 9:14-18 NIV
Paul has gone through all of this to let them know what an apostle could require of them. He also wants them to understand that he has not used any of these rights for his own benefit nor does he want to use them now. Paul is going to preach the gospel, not for pay, but because his love for Jesus compels him to do so. He preaches voluntarily to lay up rewards in heaven. If he or we should do so for any other reason then we are merely fulfilling our duty and there will be little or no joy in doing so. Our salvation cost us nothing, it was paid for at Calvary, we should tell others just because we love Jesus. If Paul is going to boast about anything it will be that he preaches the gospel without charging anyone for it and thus he will retain his reward. Each of us should feel the same way in using the gift that God has given each of us as a member of His body.
8 Heal the sick, raise the dead, cleanse those who have leprosy, drive out demons. Freely you have received; freely give.—Matt. 10:8 NIV