Catechism of the Catholic Church
a and b. Para. 787: 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 (Cf. Mk 1:16-20; 3:13-19; Mt 13:10-17; Lk 10:17-20; 22:28-30). 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" (Jn 15:4-5). 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" (Jn 6:56).
Para. 788: When his visible presence was taken from them, Jesus did not leave his disciples orphans. He promised to remain with them until the end of time; he sent them his Spirit (Cf. Jn 14:18; 20:22; Mt 28:20; Acts 2:33). As a result communion with Jesus has become, in a way, more intense: "By communicating his Spirit, Christ mystically constitutes as his body those brothers of his who are called together from every nation" (LG 7).