Saint Maximilian Kolbe: "Some are incapable of marriage"

... because they have renounced marriage for the sake of the Kingdom of heaven.

-- Mt 19:3-12

Christ proposes the evangelical counsels, in their great variety, to every disciple. The perfection of charity, to which all the faithful are called, entails for those who freely follow the call to consecrated life the obligation of practicing chastity in celibacy for the sake of the Kingdom, poverty and obedience. It is the profession of these counsels, within a permanent state of life recognized by the Church, that characterizes the life consecrated to God.

-- CCC 915