By the oblation of Jesus Christ in the Mass, we offer to God a complete satisfaction for all the sins of men, and especially for the sins of those who are present at Mass ; to whom is applied the same divine blood, by which the human race was redeemed on Calvary.
Thus, by each Mass more satisfaction is made to God than by any other expiatory work. But although the Mass is of infinite value, God accepts it only in a finite manner, according to the dispositions of those who attend the holy sacrifice, and, therefore, it is useful to hear several Masses.
--St. Alphonsus Liguori,
The Holy Eucharist
The celebration of Holy Mass is as valuable as the death of Jesus on the cross. 
The angels surround and help the priest when he is celebrating Mass. 
When the Eucharist is being celebrated, the sanctuary is filled with countless angels who adore the divine victim immolated on the altar. 
By the oblation of Jesus Christ in the Mass, we offer to God a complete satisfaction for all the sins of men, and especially for the sins of those who are present at Mass ; to whom is applied the same divine blood, by which the human race was redeemed on Calvary.
