Commentaries:
The original Greek word translated "through" here would better be translated "because of": "Ye know that because of an infirmity of my flesh I preached . . ." (KJV). Some sort of physical ailment derailed his original plans, and due to being restrained or hindered, he preached the gospel to them. This appears to be another example of Proverbs 16:9: "A man's heart plans his way, but the LORD directs his steps." Paul's original teaching to the Galatians could seem "accidental" in that circumstances beyond Paul's control dictated his location and activity, but it is apparent that the sovereign God was in control, ensuring that the gospel would be preached to those He had chosen.
David C. Grabbe