Catechism of the Catholic Church

From the beginning, Jesus associated his disciples with his own life, revealed the mystery of the Kingdom to them, and gave them a share in his mission, joy, and sufferings. Jesus spoke of a still more intimate communion between him and those who would follow him: "Abide in me, and I in you.... I am the vine, you are the branches." And he proclaimed a mysterious and real communion between his own body and ours: "He who eats my flesh and drinks my blood abides in me, and I in him." (755)