nēsteuō

In everyday Greek this word simply meant to go without eating, and it could describe anyone who was hungry or had not had a meal. But by the time of the New Testament it had become a religious term. The Greek translation of the Old Testament had used it, again and again, for the Hebrew practice of fasting before God, and that steady use fixed its meaning. So when the Gospels and Acts use it, they are never talking about dieting or ordinary hunger. They mean deliberately abstaining from food as a way of humbling oneself, praying more intently, mourning, or seeking God's guidance.

In the Bible only one fast was actually commanded, the Day of Atonement. Every other fast was voluntary, chosen by an individual or a community in response to grief, danger, repentance, or longing. That is the world these New Testament verses assume. When the Pharisee in Jesus' parable boasts that he fasts twice a week, he is describing an extra, self-imposed discipline that went beyond what the Law required, not a rule everyone kept.

Jesus treats fasting as normal and good, but he refuses to let it become a performance. In the Sermon on the Mount he does not tell his followers whether to fast; he assumes they will, and warns them not to make their faces gloomy to advertise it. His most striking teaching ties fasting to himself: while he is present with his disciples, like guests at a wedding, it is a time for joy, not fasting; a day is coming when he is taken away, and then they will fast. The early church picked this up, fasting together when they sought God's direction and set people apart for their work.

Because fasting is almost always paired with prayer in these passages, the word carries the idea of dependence on God rather than mere self-denial. It is the body's way of joining the heart in asking, mourning, or waiting.