Firmissimam Constantiam §10

¹⁰ But the magnitude of the work must not cause you to preoccupy yourselves more than the number of collaborators than with the quality. Following the example of the Divine Master, who wished to precede the few years of His apostolic work with a long preparation, and limited Himself to forming in the Apostolic College not many but select instruments for the future conquest of the world, so you also, Venerable Brethren, should care first of all for the supernatural formation of your directors and propagandists, without being too much preoccupied or grieved because at the beginning they form but a pusillus grex ( Luke xii. 32).