To keep watch over, to guard, to observe, to hold fast. Tēreō describes both protective guarding (keeping safe) and faithful observance (keeping commandments). It implies vigilance — active, intentional holding on to what matters.
Jesus' High Priestly Prayer uses tēreō repeatedly: 'Holy Father, keep them in your name' (John 17:11). God keeps us; we keep His commands. 'If you love me, keep my commandments' (John 14:15). Jude's doxology: 'To him who is able to keep you from stumbling' (Jude 1:24). The double direction is key: we are kept by God's power and called to keep faith, creating a covenant partnership of guarding and obedience.