Near the end of Galatians Paul writes, "See what large letters I make when I am writing in my own hand!" What does the line tell us about how the letter was written?

He dictated it and took the pen for the close. Up to that line a secretary had been writing down what Paul said; now Paul writes in his own hand, and he points at the difference. He points to his own handwriting again in the greeting near the end of 1 Corinthians (1 Corinthians 16:21), and in Philemon 1:19, where he writes out a promise to repay.