At the Last Supper, Jesus celebrated his farewell meal with his disciples, the celebration of his approaching death and resurrection. It was the culmination of the entire saving mission of the Lord, as well as the assurance of the power of that very same event being ever present in time and space.
The bread, the Lord tells us, represented his body given for us, the wine his blood poured out for us. In celebrating this sacred meal with his disciples, Christ was giving to them, and to all mankind, what he had already offered to his heavenly Father, namely, his own self as a redeeming victim. All of this was accomplished through sacred signs, which continually made present this saving sacrifice so that all humankind could forever unite and share in it. Consequently, after the Ascension, when the glorified, risen Christ took his rightful place at the right hand of the Father, he did not leave us orphans but continued to act and to dispense grace through the Eucharist and the other six sacraments he had instituted during his earthly ministry. These would be sources of living grace that would flow into the hearts of all those who through faith would participate in them.
All of this is accomplished through humanly perceptible signs and symbols that not only signify grace but effect it through the power of the Holy Spirit. Initially, this saving event of Christ’s Passion, Death, and Resurrection took place in time and in history, once and for all, while simultaneously and in reality, transcending all time through the action of the Holy Spirit, the great catalyst who is always active in the liturgical life of the Church. “Christ is always present in His Church, especially in her liturgical celebrations." (Second Vatican Council, Constitution on the Sacred Liturgy Sacrosanctum Concilium (December 4, 1963), no. 7) Having come to us from the Father, Jesus now leads us back to the Father.