In a nutshell the Council tells us that the priest and laity must work together in order that the Church, the Body of Christ, may fulfil its mission to preach the gospel to every creature.
Without the priest there can be no fullness of the lay apostolate. Without the laity there can be no fullness of the priesthood for the priest must have members just as Christ himself had members.
Without the twelve, without the seventy-two, above all without Mary, there would be no Church, no Body of Christ in the modern world. Without the priest the vast potential of the laity remains untapped. A great reservoir remains just that - it does not flow into life-giving circulation. Instead it stagnates.