The Catholic Church describes the Eucharist, i.e., the Sacrifice of the Mass, as “the source and summit of the Christian life” (CCC 1324).
It’s the source, because the Eucharist enables us to make present and offer anew Jesus Christ’s one redemptive Sacrifice of Calvary, which began with his Passion (CCC 1362-68; 1341).
It’s the summit, because the Eucharist is truly a foretaste of heaven, in which we partake of Jesus’ body and blood as heaven and earth become most profoundly one.