The holy Eucharist completes the Christian initiation...The Eucharist is the efficacious sign and sublime cause of that communion in the divine life and that unity of the People of God by which the Church is kept in being.

-CCC, nos.1322 and 1325, citing
Sacred Congress of Rites, Instruction on the Worship of the Eucharistic Mystery (Eucharisticum Mysterium), no. 6