Therefore - Διὰ τοῦτο Dia touto. On account of this. That is, because the light of the gospel is so clear; because it reveals so glorious truths, and all obscurity is taken away, and we are permitted to behold as in a mirror the glory of the Lord, 2 Corinthians 3:18. Since the glories of the gospel dispensation are so great, and its effects on the heart are so transforming and purifying. The object is, to show the “effect” of being entrusted with such a ministry, on the character of his preaching.
Seeing we have this ministry - The gospel ministry, so much more glorious than that of Moses 2 Corinthians 3:6; which is the ministry by which the Holy Spirit acts on the hearts of people 2 Corinthians 3:8; which is the ministry of that system by which people are justified 2 Corinthians 3:9; and which is the ministry of a system so pure and unclouded, 2 Corinthians 3:9-11, 2 Corinthians 3:18.
As we have received mercy - Tyndale renders this: “even as mercy is sure in us.” The idea is, that it was by the mere mercy and favor of God, that he had been entrusted with the ministry, and the object of Paul is doubtless to prevent the “appearance” of arrogance and self-confidence by stating that it was to be traced entirely to God that he was put into the ministry. He doubtless had his eye on the fact that he had been a persecutor and blasphemer; and that it was by the mere favor of God that he had been converted and entrusted with the ministry, 1 Timothy 1:13. Nothing will more effectually humble a minister, and prevent his assuming any arrogant and self-confident airs, than to look over his past life; especially if his life was one of blasphemy, vice, or infidelity; and to remember that it is by the mere mercy of God that he is entrusted with the high office of an ambassador of Jesus Christ. Paul never forgot to trace his hope, his appointment to the ministerial office, and his success, to the mere grace of God.
We faint not - This is one of the effects of being entrusted with such a ministry. The word used here (ἐκκακοῦμεν ekkakoumen) means, properly, to turn out a coward; to lose one’s courage; then to be fainthearted, to faint, to despond, in view of trial, difficulty, etc. - Robinson. Here it means, that by the mercy of God, he was not disheartened by the difficulties which he met; his faith and zeal did not flag; he was enabled to be faithful, and laborious, and his courage always kept up, and his mind was filled with cheerfulness; see note on 2 Corinthians 2:14. He was deterred by no difficulties; embarrassed by no opposition; driven from his purpose by no persecution; and his strength did not fail under any trials. The consciousness of being entrusted with “such” a ministry animated him; and the mercy and grace of God sustained him.