18 We believe that it is a duty of the Church at the present time to strive toward a clearer and deeper awareness of itself and its mission in the world, and of the treasury of truth of which it is heir and custodian. Thus before embarking on the study of any particular problem and before considering what attitude to adopt vis-a-vis the world, the Church must here and now reflect on its own nature, the better to appreciate the divine plan which it is the Church's task to implement. By doing this it will find a more revealing light, new energy and increased joy in the fulfillment of its own mission, and discover better ways of augmenting the effectiveness and fruitfulness of its contacts with the world. For the Church does indeed belong to the world, even though distinguished from it by its own altogether unique characteristics .
Source: Ecclesiam Suam (Vatican.va)