38 But, while earnestly exhorting all to a friendly union of will, and beseeching God, the Prince of peace, to infuse a love of concord into all hearts, We cannot, venerable brothers, refrain from urging you more and more to fresh earnestness, and zeal, and watchfulness, though we know that these are already very great. With every effort and with all authority, strive, as much as you are able, to preserve whole and undefiled among the people committed to your charge the doctrine which Christ our Lord taught us; which the Apostles, the interpreters of the will of God, have handed down; and which the Catholic Church has herself scrupulously guarded, and commanded to be believed in all ages by the faithful of Christ.
Source: Arcanum Divinae (Vatican.va)