Don Carson on 2 Corinthians 8 (For the Love of God vol.1)
"There is considerable stress on perseverance and consistency in this matter of giving. Apparently the Corinthians had pledged the year before to give a certain amount. Now Paul sends Titus to encourage them to bring to completion what they began so well. So today: planned, regular, generous giving is better than the big binge that is wrung out of you by one emotional appeal, in part because the former is a better index of a heart consistently devoted to Christ and his work."