First is our duty to worship God. “Keep holy the Sabbath”
Our Lord on the Cross offered the greatest form of worship to His Father, as we where not at the foot of the Cross with Mary, His mother, St. Mary Magadaline, St. John and the others, He gives us the opportunity to step out of time, and stand, or kneel at the foot of the Cross in an unbloody manner and offer Himself. He is the primary and High Priest as well as victim at every Mass. Through the priest whom He has chosen, just as He chose the Apostles, Christ provides for us the Mass, not a new sacrifice, like those of the Old Testament where a different animal was sacrificed each time, but the same Sacrifice where Jesus offers Himself. A foretaste of the offering of the Lamb in the Heavenly Jerusalem, a shadow of our witnessing of the worship of God in Heaven.
Communion, fellowship, instruction, Celebration of the Triumph over death by Christ Jesus all play a role in the Mass, there are any number of Graces and good reasons for our assisting at Mass on Sundays and Holy Days of Obligation, however the greatest is that we there worship God in the manner He dictated. He told us the bread had become His Body, and the Wine His blood. He told the Apostles in the upper room to do the same thing as an anamensis of what He had done there, and what He would do on the Cross. He makes Himself and the fruits of His Passion, Death and Resurrection real to us through the Mass. He lets us give the greatest form of worship to the Father by sharing with us the ablility to transcend time and to worship the Father as He did on that great and awsome day, never to die again, but to allow His Resurrected and Glorified Body no longer bound to the laws of this world to His Father, who through our Baptism becomes our adopted Father.