tēreō

This is the most common use of the word in the New Testament, and the one that shapes how people live. To keep a command, or to keep someone's word, is not merely to remember it or agree with it. It is to guard it carefully and act on it, so that the command stays unbroken in the way you live.

Jesus uses this word again and again to tie love to obedience: those who love him keep his words, and those who keep his commands are the ones who truly know God. John's letters press the same point, testing real faith by whether a person actually keeps God's commands rather than only claiming to.

The word carries a sense of watchful care, not grudging compliance. You keep a command the way a faithful person keeps a trust: attentively, completely, and over the long haul. Breaking one part of the law is described as failing to keep the whole of it, because the keeping is meant to be entire.

Here the word is used in its plainest physical sense: to watch over someone so they cannot escape or come to harm. It is the work of soldiers and jailers. Guards keep watch over Jesus at the cross and at the tomb, and Peter and Paul are each kept under guard in prison.

This concrete, everyday picture stands behind the word's other uses. To guard a prisoner is to keep him in one place, under your eye, secure. From that physical image the word stretches naturally to keeping a command unbroken and to keeping a person safe.

This use is about safekeeping rather than custody or obedience. It covers holding something back for the right moment, keeping a person from harm, and preserving a thing in good condition. The host at Cana had kept the good wine until the end; Mary kept the costly perfume for the day of Jesus' burial; an inheritance is kept safe in heaven, beyond decay.

The protective edge is strong in prayer and promise. Jesus prays that the Father will keep his followers safe and guard them from the evil one, and he promises to keep the faithful church from the hour of trial coming on the world.

The same word can preserve for rescue or preserve for judgment: God knows how to keep the godly safe while holding the unrighteous under guard for the day of reckoning. Whether the outcome is deliverance or condemnation, the action is the same: something is held securely until its appointed time.