The Greek verb enischuo means to strengthen, to make strong within, or to invigorate — used of supernatural strengthening that renews a depleted person. It appears at two of the most intense moments of physical and spiritual exhaustion in the New Testament.
Enischuo describes divine strength poured into human weakness at its most acute. In Luke 22:43, an angel appeared to Jesus in Gethsemane and 'strengthened (enischuo) him' — the Son of God in the extremity of human anguish received supernatural fortification to face the cross. This is perhaps the most tender single act of God in the passion narrative. The second use is in Acts 9:19: after Paul's blinding and fasting, when he received food 'he regained his strength (enischuo)' — physical nourishment as divine restoration. Enischuo teaches that God does not simply command us to be strong (Ephesians 6:10); He actively pours strength into us. The strengthening is internal (the en prefix) — not external encouragement but inward renewal.