kaleō

At its plainest the word is what a parent does at a birth: it fixes a name on a person. From there it widens to how people are addressed and what they come to be known as. The same word can report the name actually given, the title others use, and the standing a name confers, since in the biblical world a name was not a label stuck on from outside but a statement of who someone is.

This is why the passive ("he will be called") so often means more than "people will say this about him." To be called the Son of God, or to be called righteous, is to be publicly acknowledged as that, even reckoned as that. The line between naming and declaring is thin here, and the word sits right on it.

Keep this naming sense apart from the inviting sense and from God's saving call: all three are the one Greek word, but they do different work, and only the surrounding sentence tells you which is meant.

This is the word for sending word that someone should come: a master summons his servants, a host invites his guests, a court calls a witness. The action is a real-world request to show up, whether it is a quiet word to one person or an open invitation to a feast.

Much of this sense clusters in stories Jesus tells about banquets, where being invited, or invited and then refusing, carries the weight of the parable. The invited guests are a settled group, "those who were called," and the drama turns on whether they come. Reading these as God's saving call gets ahead of the story, the everyday picture of a host and his guest list is doing the work, even where it points beyond itself.

In the letters of the New Testament the word takes on a particular weight: God himself is the one who calls. This is not merely an invitation left for the hearer to accept or decline, it is God reaching out and bringing a person into relationship with him, into the people he is forming, and into the life that follows from that.

The call has a destination as well as a source. People are called out of darkness, called into fellowship with Christ, called to freedom, to peace, to holiness, to one shared hope. So the word names both the decisive moment when God lays claim to someone and the kind of living that claim is meant to produce. The person who answers is, in this same family of words, one of "the called."

This sense grows out of the older naming sense: when God calls a people his own, he both gives them a new standing and brings them into being as that people. Whether a given verse is simply an invitation or this deeper divine summons is sometimes a real interpretive question, and the letters are where the heavier meaning is at home.