Haydock Catholic Bible Commentary
The ministry, that is, the contributions for the brethren, so it is also called again, (ver. 12.) the ministry of this office, or, as the Greek signifies, of this sacrifice, inasmuch as alms, and such charitable works, are spiritual sacrifices to God. (Witham)
That Achaia also was ready. Corinth was the capital of Achaia. St. Paul had formerly exhorted the Macedonians to contribute to the utmost of their power, informing them, that Corinth and all Achaia were prepared a year ago to collect alms, and now the apostle, speaking to the Corinthians, encourages them by the example of the faithful of Macedon, and informs them of the greatness of their charitable contributions, and the greatness of their zeal. (Theo.)
2Co 9:3 , and two others.
Not forced from covetousness. Literally, not as avarice, as it were extorted from covetous people, who give unwillingly. (Witham)
2Co 9:8 is generous to the liberally disposed Christian; filling such as relieve the poor with every species of good, and returning their charities a hundred-fold. (Menochius)
All bountifulness, by which is signified, a sincere and free liberality, by giving with a sincere heart, and good intention. St. Paul encourages them to contribute willingly for God's sake, and out of a true charity for their indigent brethren, who will praise, and thank God, and pray for them, &c. (Witham)
For his unspeakable gift. Such is the conclusion, which the apostle puts to the subject upon alms-deeds. In the following chapter he proceeds to a new subject; but first thanks the Almighty, that he has enriched the Corinthians with so charitable a disposition. St. John Chrysostom, Theo., and some other commentators think, that by the expression, his unspeakable gift, is meant the incarnation of Christ. The fruit of alms-deeds is the increase of grace in all justice and good works to life everlasting; God granting these blessings for a reward and recompense of charitable works, which therefore are called the seed, (ver. 10. above) or meritorious cause of these spiritual fruits.
 In omnem simplicitatem, Greek aploteta, upon which St. John Chrysostom says, Greek: om. k., aploteta ten dapsileian kalei, a plentiful abundance.