The Priest incenses the Bread and Wine in such a way, that its odour may perfume, and wholly cloud in fragrance the Things offered; while so doing, he says these words: Incesum istud a te benedictum, ascendat ad te Domine, et descendat super nos misericordia tua. May this Incese, blessed by Thee, ascend to Thee, O Lord, and may They Mercy descend upon us. This Prayer, whilst being a homage paid to God, is a wish expressed for ourselves also. The Priest divides these words, at intervals, whilst incensing the several parts to be thus honoured, in performing which ceremony, he follows what the rubrics prescribe. When he first incensed the Altar, the Priest said no Prayer; but now, when thus honouring it a second time, Holy Church bids him repeat a portion of Psalm cxl., which she selects, chiefly on account of these words which occur therein, and which are the first she puts on the lips of the Priest: Dirigantur, Domine, oratio mea sicut inceunsum in conspectu tuo. May my prayer, O Lord, ascend as incense in Thy sight. It is thus she always does, ever selecting with wonderful appropriateness whatsoever suits the circumstance, whether in Psalms, or in Gospels and Epistle.s The Priest begins by incensing the Cross, or the Most Holy Sacrament if exposed; he then bows before the Cross, or genuflects, if the Most Holy Sacrament is reserved in the Tabernacle of that Altar; then, if there be relics there exposed, he incenses them with two throws of the Thurible, first on the Gospel side, then on the Epistle side; after which he incenses every part of the Altar. In all other respects, this incensing differs in no way from the first, nor from that which is performed at Lauds and Vespers.
On returning the Thurible to the Deacon, the Priest gives expression to a good wish in his regard as well as in his own, saying: Accendat in nobis Dominus ignem sui amoris et flammam aeternae charitatis. May the Lord enkindle in us the fire of His Love and the flame of everlasting charity. On taking the Thurible, the Deacon kisses the Priests’s hand, and then the top of the chains; he does the contrary, on presenting it. These customs have come to us from the East, and, inasmuch as they are marks of reverence and respect, it is to the Liturgy we owe the preservation of them. The Deacon then honours the Priest with incense, who receives it standing sideways to the Altar; but if the Most Holy Sacrament be exposed, as, for instance, at the Mass of Reposition, the Priest comes down from the Altar, and with his face turned to the people, he receives the said honours from the Deacon, who likewise suits his position to the occasion. Then follows the incensing of the Choir, beginning with the Bishop, if present; next the Prelates, if there; then the Priests and Clerics; and finally, all of the Faithful, to show that all form but one Body, of which Jesus Christ is the Head. All, whether Bishops, Prelates, or simple Faithful, should rise on receiving the incense; the Pope alone remains seated for its reception.
[From The Holy Mass, by Dom Prosper Gueranger]