77 Yet although it remains unquestionably true that mere numbers should not be the chief concern of those engaged in the education of the clergy, yet at the same time, all should do their utmost to increase the ranks of strong and zealous workers in the vineyard of the Lord; the more so, as the moral needs of society are growing greater instead of less. Of all the means to this noble end, the easiest and the most effective is prayer. This is, moreover, a means within the power of everyone. It should be assiduously used by all, as it was enjoined by Jesus Christ Himself: "The harvest, indeed, is great but the laborers are few. Pray ye, therefore, the Lord of the harvest, that He send forth laborers into His harvest." What prayer could be more acceptable to the Sacred Heart of our Savior? What prayer is more likely to be answered as promptly and bounteously as this, which meets so nearly the burning desire of that Divine Heart?" "Ask therefore, and it will be given unto you"; ask for good and holy priests and Our Lord will not refuse to send them to His Church, as ever He has done throughout the centuries. It has been, in fact, precisely in times which seemed least propitious, that the number of priestly vocations increased. This is clear from Catholic hagiography of the nineteenth century a century rich in splendid names on the rolls both of secular and regular clergy. One has only to think of those three splendid saints whom We Ourselves had the consolation of canonizing - St. John Mary Vianney, St. Joseph Benedict Cottolengo and St. John Bosco, men of truly lofty holiness, each in his special way.
Source: Ad Catholici Sacerdotii (Vatican.va)