Hortus conclusus es, Dei Genetrix: hortus conclusus, fons signatus: surge, propera, amica mea.
“Thou art an enclosed garden, Mother of God: an enclosed garden, a fountain sealed up: rise, make haste, my beloved.”
This antiphon comes from the Divine Office of the Immaculate Conception. We chant these words to the Blessed Virgin, addressing her as hortus conclusus, an “enclosed garden.” This phrase originally comes from the Scriptures, namely from the Song of Songs. The Church has taken these sacred words and applied to the Blessed Virgin. Why is this so?
The Song of Songs is on the surface a love poem between a man and woman who are smitten with one another. These lovers, the bride and the bridedgroom, alternate in declarations of their infatuation and descriptions of each other’s beauty replete with exotic comparisons to cypress trees, vineyards, spikenard, gazelles, and similar exotic imagery (e.g. Thy cheeks are as a piece of a pomegranate; Thy neck is as a tower of ivory; thine eyes like the fishpools in Heshbon, by the gate of Bathrabbim). But, being a divinely inspired book of the scriptures, there is hidden beneath the surface of these vivid images a profound revelation: that of God’s unfathomable love. Many saints and other masterly commentators on this divine love poem have recognized three mystical relations being described: the relation between Christ and the Church; between Christ and the soul; and specifically between Christ and the Blessed Virgin Mary.
God has love for all his creation, but it is especially occupied with the Blessed Virgin Mary. This is most clear from the fact that he chose her from among all women to be his own mother. He prepared her for this unique role by preserving her from all stain of sin, by bestowing on her the grace to be immaculately conceived. Hence the words from the Song of Songs, "Thou art all fair, O my love, and there is not a spot in thee," are aptly applied to the Holy Virgin; no spot of sin ever blighted the all-fair Virgin. Likewise, to return to the antiphon above, Our Lady is fittingly described as a hortus conclusus, an enclosed garden, because of the special divine graces she received.
Mary is an enclosed garden because of her perpetual virginity. When she was told that she would conceive the Son of God in her womb Mary responded to the archangel Gabriel, "How can this be since I do not know man?" The archangel revealed that the Holy Spirit himself would overshadow the Virgin and marvelously conceive Jesus Christ. The garden of Mary’s womb was thus only accessible by Almighty God and was closed off to all others. Mary is a paradisiacal garden—a new sort of Eden—reserved for God alone, and the fruit of her womb—a new sort of Tree of Life—is the incarnate Son of God himself. And thus in wonder and admiration, and in the very expressions of love uttered by God himself in the Song of Songs, we chant the praises of the hortus conclusus, the enclosed garden of the Blessed Virgin Mary.
The following verses from the Song of Songs are those set to music in the piece "Hortus Conclusus."
 Quam pulchra es, amica mea! quam pulchra es! Oculi tui columbarum, absque eo quod intrinsecus latet. Capilli tui sicut greges caprarum quae ascenderunt de monte Galaad.  Dentes tui sicut greges tonsarum quae ascenderunt de lavacro; omnes gemellis foetibus, et sterilis non est inter eas.  Sicut vitta coccinea labia tua, et eloquium tuum dulce. Sicut fragmen mali punici, ita genae tuae, absque eo quod intrinsecus latet.  Sicut turris David collum tuum, quae aedificata est cum propugnaculis; mille clypei pendant ex ea, omnis armatura fortium.  Duo ubera tua sicut duo hinnuli, capreae gemelli, qui pascuntur in liliis.  Donec aspiret dies, et inclinentur umbrae, vadam ad montem myrrhae, et ad collem thuris.  Tota pulchra es, amica mea, et macula non est in te.
 Veni de Libano, sponsa mea : veni de Libano, veni, coronaberis: de capite Amana, de vertice Sanir et Hermon, de cubilibus leonum, de montibus pardorum.  Vulnerasti cor meum, soror mea, sponsa; vulnerasti cor meum in uno oculorum tuorum, et in uno crine colli tui.  Quam pulchrae sunt mammae tuae, soror mea sponsa! pulchriora sunt ubera tua vino, et odor unguentorum tuorum super omnia aromata.  Favus distillans labia tua, sponsa; mel et lac sub lingua tua : et odor vestimentorum tuorum sicut odor thuris.  Hortus conclusus soror mea, sponsa, hortus conclusus, fons signatus.
 How beautiful art thou, my love, how beautiful art thou! thy eyes are dove's eyes, besides what is hid within. Thy hair is as flocks of goats, which Come up from mount Galaad.  Thy teeth as flocks of sheep, that are shorn which come up from the washing, all with twins, and there is none barren among them.  Thy lips are as a scarlet lace: and thy speech sweet. Thy cheeks are as a piece of a pomegranate, besides that which lieth hid within.  Thy neck, is as the tower of David, which is built with bulwarks: a thousand bucklers hang upon it, all the armour of valiant men.  Thy two breasts like two young roes that are twins, which feed among the lilies.  Till the day break, and the shadows retire, I will go to the mountain of myrrh, and to the hill of frankincense.
 Thou art all fair, O my love, and there is not a spot in thee.  Come from Libanus, my spouse, come from Libanus, come: thou shalt be crowned from the top of Amana, from the top of Sanir and Hermon, from the dens of the lions, from the mountains of the leopards.  Thou hast wounded my heart, my sister, my spouse, thou hast wounded my heart with one of thy eyes, and with one hair of thy neck.  How beautiful are thy breasts, my sister, my spouse! thy breasts are more beautiful than wine, and the sweet smell of thy ointments above all aromatical spices.  Thy lips, my spouse, are as a dropping honeycomb, honey and milk are under thy tongue; and the smell of thy garments, as the smell of frankincense.  My sister, my spouse, is a garden enclosed, a garden enclosed, a fountain sealed up.