The Church is called a mystical body having Christ as its head. Saint Paul is the foremost exponent of this doctrine (1 Corinthians 6,12, 12-14,20, 27; Ephesians 4,11-13,15-16; Colossians 1,18, 24). It is chiefly this: Christ as the head of the Church exercises in a mystical, supernatural manner the same life-giving influence of the Church as the human head in the human organism. From Christ proceeds that supernatural life which unites the members among themselves and with Him. Growth, increase, both intensively (sanctity), and extensively (in numbers) depends on this vivifying union, which is fostered and preserved principally by the Holy Eucharist. Notwithstanding number and diversity of members, there is but one body.