Henri Nouwen, with Thomas Merton, were the first 20th century Catholic writers on Christian Spirituality to be widely read among non-Catholics. (And each of them was criticized for 'never having an unpublished thought.' 'Like Merton', says this biographer, [Nouwen] seemed to feel that, unless he was writing things, he wasn't fully experiencing them. There was a gravitation in both men towards writing too much.'). Many evangelicals, after reading some of Nouwen's books, didn't know they were exposing their minds to the spiritual theology of a Roman Catholic! 'It was possible for him to speak in the morning to a group of left-wing Catholic liberation theologians, lead a lunch-time seminar with Nonconformists, and in the afternoon exhort members of the Religious Right'.
I had assumed he was a Dutch Protestant rather than an American Roman Catholic.