A favourite quote from the current pope, on how the church’s holiness must be patterned after the holiness of Christ, which continually shocks and surprises us, cutting against the grain of our human expectations of “purity”:

“On the contrary, this holiness expressed itself precisely as mingling with the sinners whom Jesus drew into his vicinity; as mingling to the point where he himself was made “to be sin” and bore the curse of the law in execution as a criminal – complete community of fate with the lost (cf. 2 Cor. 5:21; Gal. 3:13). He has drawn sin to himself, made it his lot and so revealed what true “holiness” is: not separation but union, not judgment but redeeming love. Is the Church not simply the continuation of God’s deliberate plunge into human wretchedness; is it not simply the continuation of Jesus’ habit of sitting at table with sinner, of his mingling with the misery of sin to the point where he actually seeems to sink under its weight? Is there not revealed in the unholy holiness of the Church, as opposed to man’s expectation of purity, God’s true holiness, which is love, love which does not keep its distance in a sort of aristocratic, untouchable purity but mixes with the dirt of the world, in order thus to overcome it? Can therefore the holiness of the Church be anything else but the mutual support which comes, of course, from the fact that all of us are supported by Christ? I must admit that to me this unholy holiness of the Church has in itself something infinitely comforting about it.”

-Joseph Cardinal Ratzinger, Introduction to Christianity, p. 264-5.