Explanation of the Prayers and Ceremonies of Holy Mass, Dom Prosper Guéranger - Incensing of Altar

The Altar represents our Lord Jesus Christ.  The Saints' Relics which are there, remind us that the Saints are His members.  For, having assumed our human nature, He not only suffered His Passion, triumphed in His Resurrection, and entered into His glory by the Ascension, - but He, also, founded the Church upon earth, and this Church is His mystical Body; He is its Head, and the Saints are its members.  From this point of view, then, our Lord has not the fullness of His mystical Body without His Saints; and it is for this reason, that the Saints, who are reigning with Him in glory, are united with Him, in the Altar, which represents Him.

The Priest, having finished the prayer, which he said bowing down, and his hands joined on the Altar, prepares for its Incensing.  Twice will this take place during the Holy Sacrifice, and both times with much solemnity, out of respect for our Lord, who is signified by the Altar, as we have already said.  Nevertheless, the Priest does not recite any prayer during the first Incensing; he merely thurifies every portion of the Altar, in such wise as that the whole of it is thus honoured.  We learn from the Book of Leviticus, that Incense was used, at a very early period, in the divine worship.  The blessing, which the Priest gives it in the Mass, raises this production of nature to the supernatural order.  Holy Church has borrowed this ceremony from heaven itself; where St. John witnessed it.  In his Apocalypse, he saw an Angel, standing, with a golden censer, near the Altar, on which was the Lamb, with four-and-twenty elders around him. (Apoc. viii. 3.)  He describes this Angel to us, as offering to God the prayers of the Saints, which are symbolised by the incense.  Thus, our holy Mother the Church, the faithful Bride of Christ, wishes to do as heaven does; and taking advantage of the veil of its mysterious secrets being even thus partially raised up by the Beloved Disciple, she borrows, for our earth's imitation, the tribute of honour thus paid, yonder above, to the glory of her Spouse.  At this part of the Mass, the Altar alone, and the Priest, are thurified; the incensing of the Choir is reserved for the second time of the ceremony, which is at the Offertory.  - It is one of the customs of the Church to expose, on the Altar, images and relics of the Saints, which then are incensed at the same time.