The language of vocation, of being called to a way of life, has its origin in the Bible. The God of the Jews is both supremely Other – the sole origin and ruler of everything that is – and also supremely personal: knowing, loving and guiding his creatures in every detail of their lives.
He is a God outside time (unlike, for example, the gods of ancient Greece), who yet reveals himself within history, above all in the history of his chosen people.
He is a God who demands unswerving worship and loyalty, and a God of justice and merciful love.
We should not be surprised, then, by the model of vocation we find in the Old Testament: a personal summons, based on supreme authority, to a specific person, for a specific task, in the service of God’s guidance of Israel.
His servants are summoned, perhaps out of the blue, like the shepherd Amos.
Sometimes they are prepared by God beforehand: Jeremiah in his mother’s womb, Isaiah whose lips were cleansed with burning coal.
Some obey without hesitation; others, like Moses, a rabbi before his time, raise objections before they embrace their task.
The task they are called to is never one they seek. It is always demanding, usually arouses fierce opposition, sometimes leads to terrible suffering, as with Jeremiah.
Those called are answerable to God alone, and their mission – as patriarch or as prophet – is to further the reign of God among his people.
Many things will change with the coming of Christ, but the fundamentals of vocation are already in place.