In these verses the apostle speaks very respectfully to the Corinthians, and with great skill; and, while he seems to excuse his urging them so earnestly to charity, still presses them thereto, and shows how much his heart was set upon this matter.
I. He tells them it was needless to press them with further arguments to afford relief to their poor brethren (Co2 9:1), being satisfied he had said enough already to prevail with those of whom he had so good an opinion. For, 1. He knew their forwardness to every good work, and how they had begun this good work a year ago, insomuch that, 2. He had boasted of their zeal to the Macedonians, and this had provoked many of them to do as they had done. Wherefore he was persuaded, that, as they had begun well, they would go on well; and so, commending them for what they had done, he lays an obligation on them to proceed and persevere.
II. He seems to apologize for sending Titus and the other brethren to them. He is unwilling they should be offended at him for this, as if he were too earnest, and pressed too hard upon them; and tells the true reasons why he sent them, namely, 1. That, having this timely notice, they might be fully ready (Co2 9:3), and not surprised with hasty demands, when he should come to them. When we would have others to do that which is good we must act towards them prudently and tenderly, and give them time. 2. That he might not be ashamed of his boasting concerning them, if they should be found unready, Co2 9:3, Co2 9:4. He intimates that some from Macedonia might haply come with him: and, if the collection should not then be made, this would make him, not to say them, ashamed, considering the boasting of the apostle concerning them. Thus careful was he to preserve their reputation and his own. Note, Christians should consult the reputation of their profession, and endeavour to adorn the doctrine of God our Saviour.

I know the forwardness of your mind - You have already firmly purposed to contribute to the support of the poor and suffering saints.
That Achaia was ready a year ago - The whole of the Morea was anciently called Achaia, the capital of which was Corinth. The apostle means, not only Corinth, but other Churches in different parts about Corinth; we know there was a Church at Cenchrea, one of the ports on the Corinthian Isthmus.
Your zeal hath provoked very many - Hearing that the Corinthians were so intent on the relief of the sufferers in Palestine, other Churches, and especially they of Macedonia, came forward the more promptly and liberally.

For I know the forwardness of your mind,.... How that they were willing of themselves to engage in this good work; how readily they came into it; what a cheerful disposition of mind they showed towards it; and how forward they were to begin the collection:

for which I boast of you to them of Macedonia; he had one it before, which had put them upon the like service, and he still continued to boast of them,

that Achaia was ready a year ago: not that their collection was ready made so long ago; but they had shown a readiness of mind, as to every good work, so to this of communicating to the saints a year ago, when they made a beginning, though as yet had not finished. By Achaia is meant, the inhabitants of Achaia. The Arabic version renders it, the citizens of Achaia; of this country; see Gill on Act 18:12. It is sometimes taken in a large sense, and designs Greece, and includes the countries of Doris, Hellas, Aetolia, Locri, Phocis, Boeotia, Attica, and Megaris; and had its name, as some say, from the frequent inundation of waters; and others, from one of the three generals of the Pelasgi, who were of this name; and sometimes it is taken strictly and properly for the country of the Peloponnesus, or the Morea. And so Drusius, out of Hesychius, has observed, that the Achaeans were Greeks; but properly they were they that inhabited that part of Peloponnesus, called Achaia; and these seem to be intended here. The Gospel was preached in these parts with success; Epaenetus, whom the Apostle Paul salutes, Rom 16:5 and the house of Stephanas he mentions, Co1 16:15 were the firstfruits of it; and in process of time several churches were here gathered, and which continued for several ages. In the "second" century there was a synod in Achaia, concerning the time of keeping Easter, in which Bacchylus, bishop of Corinth, presided; in the beginning of the "fourth" century, the bishops of Achaia were present at the council of Nice, and in the same century bishops out of this country assisted at the synod in Sardica; in the "fifth" century there were many churches in Achaia, and the bishops of them were present in the Chalcedon synod; out of this country went several bishops, in the "seventh" century, to Constantinople, and were in the sixth synod there; and in the "eighth" century there were bishops of Achaia in the Nicene synod (d): here by Achaia are designed the churches of Christ, which were in that part of Greece in which Corinth stood, and of which that was the metropolis; so that when the apostle says Achaia was ready, his meaning is more particularly, that the Corinthians were ready:

and, adds he,

your zeal hath provoked very many: or "the zeal which is of you"; which sprung from, and was occasioned by them; for not the zeal of the Corinthians is here intended, as seems at first view, but that emulation which was stirred up in some of the leading persons among the Macedonians, upon hearing how ready they at Corinth were to minister to the necessitous brethren; and the zeal which appeared in these principal men, which was very warm, and yet prudent and seasonable, wrought very much on the minds of others, who, led by their example, contributed in a very generous and unexpected manner. In the Greek text it is, "the zeal out of you"; or, as the Arabic version renders it, "the zeal that arose from you", which was occasioned by them.

(d) Hist. Eccles. Magdeburg. cent. 2. c. 9. p. 125. cent. 4. c. 2. p. 5. c. 9. p. 425. cent. 5. c. 2. p. 6. cent. 7. c. 10. p. 258. cent. 9. c. 2. p. 7.

ready a year ago--to send off the money, owing to the apostle's former exhortation (Co1 16:1-2).

your zeal--Greek, "the zeal from you," that is, on your part; propagated from you to others.

provoked--that is, stimulated.

very many--Greek, "the greater number," namely, of the Macedonians.