From the First Book of the Rationale Divinorum Officiorum of Wm. Durandus of Mende, late 13th century:
In some churches two eggs of ostriches and other things which cause admiration, and which are rarely seen, are accustomed to be suspended: that by their means the people may be drawn to church, and have their minds more affected.From the Voyage Liturgique of Sieur de Moleon*, 1718:
Again, some say that the ostrich, as being a forgetful bird, leaveth her eggs in the dust (Job 39.14): and at length, when she beholdeth a certain star, returneth unto them, and cheereth them by her presence. Therefore the eggs of ostriches are hung in churches to signify that man, being left of God on account of his sins, if at length he be illuminated by the Divine Light, remembereth his faults and returneth to Him, Who by looking on him with His Mercy cherisheth him. As it is written in Luke that after Peter had denied Christ, the Lord turned and looked upon Peter. Therefore be the aforesaid eggs suspended in churches, this signifying that man easily forgetteth God, unless being illuminated by a star, that is, by the influence of the Holy Spirit, he is reminded to return to Him by good works.
At the conclusion of Matins [at the Church of St. Maurice in Angers on Easter Day] two chaplains take their place behind the altar curtains. Two corbeliers in dalmatics, amices, and mitellæ, with gloves on their hands, present themselves before the altar. The chaplains chant, Quem quæritis? The corbeliers representing the Maries, reply Jesum Nazarenum Crucifixum. The others answer, Resurrexit, non est hic. The corbeliers take from the altar two ostrich eggs wrapped in silk, and go forth chanting, Alleluis Resurrexit Dominus, resurrexit Leo Fortis, Christus, Filius Dei.*A pseudonym. The actual author was Jean Baptiste de Brun Desmarets: He was born in 1650, and received his education at the Monastery of Port Royal des Champs, with the monks of which order he kept up such a connection, that he was finally involved in their ruin. [The monastery was suppressed, and then razed, in the early 18th century for its Jansenist and Cartesian errors.] His papers were seized; and he was himself committed to the Bastille, and imprisoned there five years.