11 We exhort you, therefore, Venerable Brethren, again and again, - you who are called to share in Our solicitude - that with one accord you sedulously and earnestly strive to aid the Apostolic missions, putting your trust in God, and not allowing yourselves to be deterred by any difficulty. The salvation of souls is at stake, for which Our Saviour laid down His life, and appointed us bishops and priests to the work of the saints, for the perfecting of His body. Wherefore, while each one remains at the post where God has placed him, and guards the flock that God has entrusted to him, let us endeavour to the utmost that the holy missions may be furnished with those supports of which We have spoken as having been in use since the beginnings of the Church, namely, the preaching of the Gospel and the prayers and alms of pious men.
Source: Sancta Dei Civitas (Vatican.va)