34 Finally, my brethren, rejoice in the Lord always; again I will say, Rejoice: for your redemption has drawn near, and the heavenly host of the Angels is waiting for your salvation. And there is now the voice of one crying in the wilderness, Prepare ye the way of the Lord; and the Prophet cries, Ho, you that thirst, come ye to the water; and immediately afterwards, Hearken unto me, and you shall eat that which is good, and your soul shall delight itself in good things. And within a little while you shall hear that excellent lesson which says, Shine, shine, O thou new Jerusalem; for your light has come. Of this Jerusalem the prophet has said, And afterwards you shall be called the city of righteousness, Zion, the faithful mother of cities; because of the law which went forth out of Zion, and the word of the Lord from Jerusalem, which word has from hence been showered forth on the whole world.
To her the Prophet also says concerning you, Lift up your eyes round about, and behold your children gathered together; and she answers, saying, Who are these that fly as a cloud, and as doves with their young ones to me? (clouds because of their spiritual nature, and doves, from their purity). And again, she says, Who knows such things? Or who has seen it thus? Did ever a land bring forth in one day? Or was ever a nation born all at once? For as soon as Zion travailed, she brought forth her children. And all things shall be filled with joy unspeakable because of the Lord who said, Behold, I create Jerusalem a rejoicing, and her people a joy.
Source: Catechetical Lectures (New Advent)