"Again, think ye that we are excusing ourselves unto you?"
Do you see how he is continually in fear, lest he should incur the suspicion of flattery? Do you see an Apostle's prudence, how constantly he mentions this? For he said before, "We commend not ourselves again, but give you occasion to glory;" [2 Corinthians 5:12] and in the commencement of the Epistle, "Do we need letters of commendation?" [2 Corinthians 3:1]
"But all things are for your edifying." Again he is soothing them. And he does not here either say clearly, 'on this account we receive not, because of your weakness;' but, 'in order that we may edify you;' speaking out indeed more clearly than he did before, and revealing that wherewith he travailed; but yet without severity. For he did not say, 'because of your weakness;' but, 'that you may be edified.'
[AD 384] Ambrosiaster on 2 Corinthians 12:19