In fact, he will explicitly define himself

as "apostle by vocation" (cf. Rom 1: 1; I Cor 1: 1) or "apostle by the will of God" (II Cor 1: 1; Eph 1: 1; Col 1: 1), as if to emphasize that his conversion was not the result of a development of thought or reflection, but the fruit of divine intervention, an unforeseeable, divine grace.

Pope Benedict XVI