How is it possible that it requires a specific vocation to be a member of a prelature?

Naturally this vocational requirement is not essential to personal prelatures, which could be based on very diverse circumstances, usually linked to social bonds among its faithful.

Personal prelature
Opus Dei - How is it possible that it requires a specific vocation to be a member of a prelature?

Naturally this vocational requirement is not essential to personal prelatures, which could be based on very diverse circumstances, usually linked to social bonds among its faithful.

Nevertheless, a vocation could be required if the ecclesial reality itself entailed a specific vocation, which is true in the case of Opus Dei. The Church recognizes and fosters a reality that comes from the Holy Spirit, without whose help the whole prelature of Opus Dei would cease to exist.