26 These things being so, my Eustochium, daughter, lady, fellow-servant, sister— these names refer the first to your age, the second to your rank, the third to your religious vocation, the last to the place which you hold in my affection— hear the words of Isaiah: “Come, my people, enter thou into your chambers, and shut your doors about you: hide yourself as it were for a little moment, until the indignation” of the Lord “be overpast.” Let foolish virgins stray abroad, but for your part stay at home with the Bridegroom; for if you shut your door, and, according to the precept of the Gospel, pray to your Father in secret, He will come and knock, saying: “Behold, I stand at the door and knock; if any man...open the door, I will come in to him, and will sup with him, and he with me.” Then straightway you will eagerly reply: “It is the voice of my beloved that knocks, saying, Open to me, my sister, my love, my dove, my undefiled.”
It is impossible that you should refuse, and say: “I have put off my coat; how shall I put it on? I have washed my feet; how shall I defile them?” Arise immediately and open. Otherwise while you linger He may pass on and you may have mournfully to say: “I opened to my beloved, but my beloved had gone.” Why need the doors of your heart be closed to the Bridegroom? Let them be open to Christ but closed to the devil according to the saying: “If the spirit of him who has power rise up against you, leave not your place.” Daniel, in that upper story to which he withdrew when he could no longer continue below, had his windows open toward Jerusalem. Do you too keep your windows open, but only on the side where light may enter and whence you may see the eye of the Lord.
Open not those other windows of which the prophet says: “Death has come up into our windows.”
Source: Letters (New Advent)