768 It is a strange thing that although the soul which experiences this union with God cannot find words and expressions to describe it, nevertheless, when it meets a similar soul, the two understand each other extraordinarily well in regard to these matters, even though they speak but little with each other. A soul united with God in this way easily recognizes a similar soul, even if the latter has not revealed its interior [life] to it, but merely speaks in an ordinary way. It is a kind of spiritual kinship. Souls united with God in this way are few, fewer than we think.
769 I have noticed that the Lord grants this grace to souls for two purposes. The first is when the soul is to do some great work which is, humanly speaking, absolutely beyond its power. In the second case, I have noticed that the Lord grants it in order that kindred souls might be guided and set at peace, although the Lord can grant this grace as He pleases and to whomever He pleases. However, I have noticed this grace in three priests, one of whom is a secular priest [probably Father Sopocko] and the other two, religious priests [probably Father Elter and Father Andrasz], and also in two religious sisters [probably Mother Michael and Sister Mary Joseph], but not in the same degree.
Diary of St. Maria Faustina Kowalska,