Lifting right from Lumen Gentium, Pope Paul VI retells the restoration by the council bishops, righting the unfortunate situation in which the Church’s traditional minsitry of service was subsumed into a stepping stone for clergy.
For this reason, at the third session of the Council, in October 1964, the Fathers ratified the principle of the renewal of the diaconate, and the following November the Dogmatic Constitution on the Church, Lumen Gentium, was promulgated. In the 19th article of this document a description is given of the principal characteristics proper to that state. “At a lower level of the hierarchy are deacons, who receive the imposition of hands ‘not unto the priesthood. but unto the ministry.’ For strengthened by sacramental race they are dedicated to the people of God, in conjunction with the bishop and his body of priests, in the service of the liturgy, of the Gospel, and of works of charity.” (Lumen Gentium 29)
The same constitution made the following declaration about permanency in the rank of deacon “These duties (of deacons), so very necessary for the life of the Church, can in many areas be fulfilled only with difficulty according to the prevailing discipline of the Latin Church. For this reason, the diaconate can in the future be restored as a proper and permanent rank of the hierarchy.” (Lumen Gentium 29)
Vatican II didn’t explicitly restore the permanent diaconate. The council bishops left the particulars to committee work in the years that would follow. This second instruction from Paul VI is what got things moving.