III. Ordinees must be carefully selected with especial reference to the Canons of the church.
And so, dear brother, hold with vigilance the helm entrusted to you, and direct your mind's gaze around on all which you see put in your charge, guarding what will conduce to your reward and resisting those who strive to upset the discipline of the canons. The sanction of God's law must be respected, and the decrees of the canons should be more especially kept. Throughout the provinces committed to you let such priests be consecrated to the Lord as are commended only by their deserving life and position among the clergy.
Permit no licence to personal favour, nor to canvassing, nor to purchased votes. Let the cases of those who are to be ordained be investigated carefully and let them be trained in the discipline of the Church through a considerable period of their life. But if all the requirements of the holy Fathers are found in them, and if they have observed all that we read the blessed Apostle Paul to have enjoined on such, viz., that he be the husband of one wife, and that she was a virgin when he married her, as the authority of God's law requires, [then ordain them].
And this we are extremely anxious should be observed, so as to do away with all place for excuses, lest any one should believe himself able to attain to the priesthood who has taken a wife before he obtained the grace of Christ, and on her decease joined himself to another after baptism. Seeing that the former wife cannot be ignored, nor the previous marriage put out of the reckoning, and that he is as much the father of the children whom he begot by that wife before baptism as he is of those whom he is known to have begotten by the second after baptism. For as sins and things which are known to be unlawful are washed away in the font of baptism, so what are allowed or lawful are not done away.
Source: Letters (New Advent)