"GOD," says Christ, "is a spirit, and they who adore Him, must adore Him in spirit and truth." In spirit, that is, with a knowledge of the nature of the worship to render Him: in truth, that is, with all the sincerity of our hearts. But tho Mass is the principal act of Divine worship; we must therefore understand it, and join with all our hearts and souls in offering it up. St, Peter warns all Christians to be ever ready to give an account of their faith, and of the motives of it. "Be ever ready," says be, "to satisfy every one that asketh you the reason of the hope that is in you." This warning particularly regards the Sacrifice of the Mass, which is a principal Christian mystery, nay, all abridgment of all mysteries. "Let your worship," says St. Paul, "be a reasonable one." In order to this, we must understand the nature of sacrifice ill general, and of the Sacrifice of the Mass in particular; we must know what are the intentions and dispositions necessary in order that the Mass may become available to us.