'Mighty' in the Bible

The weapons of our warfare are not physical [weapons of flesh and blood]. Our weapons are divinely powerful for the destruction of fortresses.

The signs that indicate a genuine apostle were performed among you fully and most patiently—signs and wonders and miracles.

since you seek [forensic] proof that Christ is speaking in and through me. He is not weak or ineffective in dealing with you, but powerful within you.