3 In this way I wish principally to achieve two objectives of no little importance: on the one hand, to pay homage to this historic document of Paul VI and to its teaching; on the other hand, following in the footsteps of my esteemed predecessors in the See of Peter, to reaffirm the continuity of the social doctrine as well as its constant renewal. In effect, continuity and renewal are a proof of the perennial value of the teaching of the Church. This twofold dimension is typical of her teaching in the social sphere. On the one hand it is constant, for it remains identical in its fundamental inspiration, in its "principles of reflection," in its "criteria of judgment," in its basic "directives for action," and above all in its vital link with the Gospel of the Lord. On the other hand, it is ever new, because it is subject to the necessary and opportune adaptations suggested by the changes in historical conditions and by the unceasing flow of the events which are the setting of the life of people and society.
Source: Sollicitudo Rei Socialis (Vatican.va)