47 Not all the sponsors of these new doctrines are carried to the extremes of unbridled lust; there are those who, striving as it were to ride a middle course, believe nevertheless that something should be conceded in our times as regards certain precepts of the divine and natural law. But these likewise, more or less wittingly, are emissaries of the great enemy who is ever seeking to sow cockle among the wheat. We, therefore, whom the Father has appointed over His field, We who are bound by Our most holy office to take care lest the good seed be choked by the weeds, believe it fitting to apply to Ourselves the most grave words of the Holy Ghost with which the Apostle Paul exhorted his beloved Timothy: "Be thou vigilant . . . Fulfill thy ministry . . . Preach the word, be instant in season, out of season, reprove, entreat, rebuke in all patience and doctrine."
Source: Casti Connubii (Vatican.va)