I do not think I have ever explained this before as clearly as here. When we are seeking God within ourselves (where He is found more effectively and more profitably than in the creatures, to quote Saint Augustine, who, after having sought Him in many places, found Him within)100 it is a great help if God grants us this favour. Do not suppose that the understanding can attain to Him, merely by trying to think of Him as within the soul, or the imagination, by picturing Him as there. This is a good habit and an excellent kind of meditation, for it is founded upon a truth -- namely, that God is within us. But it is not the kind of prayer that I have in mind, for anyone (with the help of the Lord, you understand) can practise it for himself. What I am describing is quite different. These people are sometimes in the castle before they have begun to think about God at all. I cannot say where they entered it or how they heard their Shepherd's call: it was certainly not with their ears, for outwardly such a call is not audible. They become markedly conscious that they are gradually retiring101 within themselves; anyone who experiences this will discover what I mean: I cannot explain it better. I think I have read that they are like a hedgehog or a tortoise withdrawing into itself102; and whoever wrote that must have understood it well. These creatures, however, enter within themselves whenever they like; whereas with us it is not a question of our will -- it happens only when God is pleased to grant us this favour. For my own part, I believe that, when His Majesty grants it, He does so to people who are already leaving the things of the world. I do not mean that people who are married must actually leave the world -- they can do so only in desire: His call to them is a special one and aims at making them intent upon interior things. I believe, however, that if we wish to give His Majesty free course, He will grant more than this to those whom He is beginning to call still higher.
100 Confessions, Bk. X, Chap. XXVII [or Soliloquies, Chap. XXXI: cf. St. John of the Cross: II, 33, 196, n. 9.]
101 [Lit.: "conscious of a gentle interior shrinking": encogimiento, the noun used, means "shrinkage", "contraction"; it should be distinguished from recogimiento, a word often used by St. Teresa and translated "recollection".]
102 Osuna (op. cit., Bk. VI, Chap. IV) uses this simile of the hedgehog in much the same way.