(Taken from Notes Made at the Conferences of Dom Prosper Guéranger).
When the Symbol of Faith has been chanted by the faithful, the Priest kisses the Altar, and turning towards the people, he says: Dominus vobiscum, to which the usual response is given: Et cum Spiritu tuo. Wherefore does the Priest kiss the altar? Because being on the point of turning to the Faithful, he wishes to salute them with the kiss of Christ, and Christ Himself is represented by the Altar.
Next comes the reading of the Offertory: this is a modern custom, because formerly whatever was sung by the Choir was never said at the Altar. The distinctive functions of the different clerical orders are very clearly marked at this portion of the Mass: to the Deacon it belongs to present the Paten with the Host upon it, to the Priest. The Deacon cannot consecrate, but he may carry the Holy Eucharist, he may even touch and administer It; so we are not astonished to see what he is now doing; whereas we see the Sub-Deacon remaining much further off from the Celebrant.
The Priest, on receiving the Paten and whilst offering the Host, says the Prayer: Suscipe, Sancte Pater. This Prayer dates from the Eighth or Ninth century. In order the better to understand all these Prayers which now follow, we must keep steadily before us the Sacrifice itself, although it is not as yet offered in all its august reality. As a first instance, we have in this Prayer, the Host spoken of as being presented to the Eternal Father, although our host at this moment is not yet the Divine Host Itself. And it is said that this host is without spot: immaculatam hostiam; in these words allusion is made to the victims of the Old Testament, which were obliged to be without blemish, because they were a type of Our Lord, Who was one day to appear before us as the Immaculatus.
In this Prayer the thought of the Priest runs far on, from the present moment; he is thinking of the host which will be on the Altar after Consecration, the Host which alone is the True Victim. And for whom does he offer it? Here we see the advantage of our being actually present and assisting at the Mass; for not only does the Priest offer it for himself but also for those who are surrounding him: pro omnibus circumstantibus. He continually keeps mentioning all those who are here present. But more than this; the action of the holy Sacrifice of the Mass extends so far, that the Priest speaks also of all the faithful, and takes care not to omit the dead; of these last, he presently makes mention saying: pro omnibus fidelibus Christianis vivis atque defunctis; for not only is the Sacrifice intended to give glory unto God, but it is meant likewise to procure good things for man.