That we should exhort Titus. Now this is an exhortation that is of greater force, when they learn that they are expressly summoned to duty. [1] Nor was it offensive to the Macedonians, that he was desirous to have the Corinthians as partners in beneficence. In the mean time an apology is made for Titus, that the Corinthians may not think that he pressed too hard upon them, as if he had not confidence in their good disposition. For he did that, from having been entreated, and it was rather in the name of the Macedonians, than in his own.

Footnotes

1 - "Quand ils oyent qu'on les somme nommeement et presentement de faire leur droit;" -- "When they hear that they summon them expressly and presently to do their duty."

Insomuch - The sense of this passage seems to be this, "We were encouraged by this unexpected success among the Macedonians. We were surprised at the extent of their liberality. And encouraged by this, we requested Titus to go among you and finish the collection which you had proposed and which you had begun. Lest you should be outstripped in liberality by the comparatively poor Macedonian Christians, we were anxious that you should perform what you had promised and contemplated, and we employed Titus, therefore, that he might go at once and finish the collection among you."
The same grace also - Margin, "Gift;" see the note on 2-Corinthians 8:1. The word refers to the contribution which he wished to be made.

That we desired Titus - Titus had probably laid the plan of this contribution when he was before at Corinth, according to the direction given by the apostle, 1-Corinthians 16:1, etc.
The same grace - Liberality. See the note on 2-Corinthians 8:1.

Insomuch that we desired Titus,.... Observing the very great readiness, cheerfulness, and liberality of the poor Macedonians in this matter, the apostles could do no other than desire Titus to forward, hasten, and accomplish a like liberal contribution among the Corinthians; or the sense is, that the Macedonians not only prayed with much entreaty, as in 2-Corinthians 8:4 that the apostle would be pleased to take their collection, and send or carry it to Jerusalem; but also that they would entreat Titus,
that as he had begun, so he would also finish in you the same grace also; that is, that as he had already moved this affair to the Corinthians while he was with them, and had made some progress in it, though what, through one thing or another, it had been retarded, and lay in some measure neglected; that he might be desired to go again, on purpose to complete so good a work, so acceptable to God, and so useful to the poor saints; which carries in it a new and strong argument to stir up the Corinthians to this service; since they had not only the example of the Macedonian churches, but it was even at their request that Titus was desired to go upon this errand; and to this sense read the Vulgate Latin, Syriac, and Arabic versions.

Insomuch that--As we saw the Macedonians' alacrity in giving, we could not but exhort Titus, that as we collected in Macedonia, so he in Corinth should complete the work of collecting which he had already begun there, lest ye, the wealthy people of Corinth, should be outdone in liberality by the poor Macedonians.
as he had begun--Greek, "previously begun," namely, the collection at Corinth, before the Macedonians began to contribute, during the visit to Corinth from which he had just returned.
finish in you the same grace--complete among you this act of grace or beneficence on your part.
also--as well as other things which he had to do among them [ALFORD].

We desired Titus, that as he had begun. This faithful fellow laborer of Paul, when he had gone to Corinth when Paul's first epistle was sent, had begun the collection which it commanded in 1-Corinthians 16:1. Now Paul directs that he return and complete the collection before the arrival of Paul (Acts 20:1-3).
Grace. The grace of giving.
As ye abound in everything. Instead of Macedonia setting the example to Corinth, the latter ought to have led. Their church was rich in gifts. See 1-Corinthians 1:5.
I speak not by commandment. He levies no tax by command. The giving must be free and cheerful in order to be blessed. He encourages them by the forwardness of others; the example of the Macedonian brethren, and by that of Christ.
For ye know the grace of our Lord Jesus Christ. This is the chiefest of motives to giving. Our Lord gave up all for us. He became poor that we might be rich in heavenly riches. If he gave himself for us, what shall we give for him? Compare Philippians 2:7. Christ parted with riches and took poverty; with glory and took humiliation; with bliss and took suffering, all for our sakes. The passage compares Christ's pre-existent state with that he had on earth.

As he had begun - When he was with you before.