weakness: a lack of strength, whether in a sick or failing body, in the frailty of human life, or in a position of no power
The word is built from an ordinary term for strength with a prefix that cancels it, so at its root it simply means "the absence of power." Everyday Greek used it for anything that lacked strength: a sick body, a frail old person, an empty purse, a feeble character. The New Testament inherits that whole range and does not narrow it, which is why English Bibles reach for several different words to translate it.
Most often it means plain "illness." It is the word used when crowds are healed, when a woman is bent double for years, and when Timothy is told to take a little wine for his stomach. But it also reaches deeper than any single sickness, naming the frailty built into being a creature: mortal, limited, and exposed. The letter to the Hebrews keeps both edges of this in view. The human high priests are surrounded by a weakness that includes their own sin, while Jesus shares our weakness, our creaturely limits and openness to testing, yet without any sin of his own.
Paul takes this same ordinary word and turns it inside out. In a culture that prized strength, status, and polished speech, he chooses to boast in his weakness, because that is exactly where he finds God's power coming to rest. He does not give the word a new dictionary meaning. He loads the old meaning with the weight of the cross, where Christ himself was crucified in weakness and yet lives by the power of God. So the same word can describe a fever, a funeral, and the very place where grace proves sufficient.
Nuances
Whether "the weakness of the flesh" in this verse means a real bodily illness or a moral and human weakness.
- majorityA genuine physical illness that afflicted Paul during his first visit, matching the standard everyday sense of the word "on account of illness" found in the papyri.; BDAG, s.v. ἀσθένεια; J. Louis Martyn, Galatians (Anchor Yale Bible); Richard N. Longenecker, Galatians (Word Biblical Commentary)
- minorityMoral or human weakness rather than sickness, arguing that the word joined to "flesh" never denotes illness in the medical writers.; Troy W. Martin, Journal for the Study of the New Testament 74 (1999)