1 This sacred Council has several aims in view: it desires to impart an ever increasing vigor to the Christian life of the faithful; to adapt more suitably to the needs of our own times those institutions which are subject to change; to foster whatever can promote union among all who believe in Christ; to strengthen whatever can help to call the whole of mankind into the household of the Church. The Council therefore sees particularly cogent reasons for undertaking the reform and promotion of the liturgy.
Source: Sacrosanctum Concilium (Vatican.va)