The heritage of faith entrusted to the whole of the Church
The apostles entrusted the "Sacred deposit" of the faith (the depositum fidei), contained in Sacred Scripture and Tradition, to the whole of the Church. "By adhering to [this heritage] the entire holy people, united to its pastors, remains always faithful to the teaching of the apostles, to the brotherhood, to the breaking of bread and the prayers. So, in maintaining, practising and professing the faith that has been handed on, there should be a remarkable harmony between the bishops and the faithful."
Source: Catechism of the Catholic Church (Vatican.va)