Adam Clarke on 2 Corinthians 4:15

For all things are for your sakes - We proclaim all these truths and bear all these sufferings for your sakes, thinking all our sufferings nothing if we can gain converts to Christ, and build believers up on their most holy faith.

That the abundant grace - Ἡ χαρις πλεονασασα· The abounding benefit - the copious outpouring of the gifts and graces of the Holy Spirit, by which you have been favored and enriched, may, through the thanksgiving of many, redound to the glory of God: i.e. that the gratitude of the multitudes which have been converted may keep pace with the blessings which they have received, and περισσευσῃ, abound, as these blessings have abounded.