The Greek verb ischyo means to be strong, have power, or be able. It appears about 28 times in the New Testament and is closely related to ischus (G2479, strength). It emphasizes not just the possession of power but the ability to accomplish a specific task.
Ischyo carries a distinctive flavor compared to other Greek power-words: while dynamai (G1410) emphasizes inherent capability and exousia (G1849) focuses on authority, ischyo is the muscular, active word for effective strength — the kind that gets things done. The most beloved verse using this root is Philippians 4:13: 'I can do all things (panta ischyo) through Christ who gives me strength.' The context is crucial — Paul is not promising unlimited superhuman ability but describing the learned contentment of a man who has discovered that Christ's strength is sufficient in any circumstance, whether abundant or lacking. Matthew 17:16 records the disciples' confession of weakness: 'I brought him to your disciples, but they could not (ouk ischusan) heal him.' Their failure sets up Jesus' teaching on the faith required to move mountains. The disciples' ischyo fails where faith is small; God's ischyo is unlimited.