St Augustine on anger

"... And well do you know, my excellent brother, how, in the midst of such offenses, we must watch lest hatred of any one gain a hold upon the heart, and so not only hinder us from praying to God with the door of our chamber closed, but also shut the door against God Himself; for hatred of another insidiously creeps upon us, while no one who is angry considers his anger to be unjust. For anger habitually cherished against any one becomes hatred, since the sweetness which is mingled with what appears to be righteous anger makes us detain it longer than we ought in the vessel, until the whole is soured, and the vessel itself is spoiled. Wherefore it is much better for us to forbear from anger, even when one has given us just occasion for it, than, beginning with what seems just anger against any one, to fall, through this occult tendency of passion, into hating him. We are wont to say that, in entertaining strangers, it is much better to bear the inconvenience of receiving a bad man than to run the risk of having a good man shut out, through our caution lest any bad man be admitted; but in the passions of the soul the opposite rule holds true. For it is incomparably more for our soul's welfare to shut the recesses of the heart against anger, even when it knocks with a just claim for admission, than to admit that which it will be most difficult to expel, and which will rapidly grow from a mere sapling to a strong tree. Anger dares to increase with boldness more suddenly than men suppose, for it does not blush in the dark, when the sun has gone down upon it..."

Letter to Profuturus

Pius XII on brotherhood of mankind

And first of all let us imitate the breadth of His love. For the Church, the Bride of Christ, is one; and yet so vast is the love of the divine Spouse that it embraces in His Bride the whole human race without exception. Our Savior shed His Blood precisely in order that He might reconcile men to God through the Cross, and might constrain them to unite in one body, however widely they may differ in nationality and race. True love of the Church, therefore, requires not only that we should be mutually solicitous one for another as members and sharing in their suffering but likewise that we should recognize in other men, although they are not yet joined to us in the body of the Church, our brothers in Christ according to the flesh, called, together with us, to the same eternal salvation. It is true, unfortunately, especially today, that there are are some who extol enmity, hatred and spite as if they enhanced the dignity and the worth of man. Let us, however, while we look with sorrow on the disastrous consequences of this teaching, follow our peaceful King who taught us to love not only those who are of a different nation or race, but even our enemies. While Our heart overflows with the sweetness of the teaching of the Apostle of the Gentiles, We extol with him the length, and the breadth, and the height, and the depth of the charity of Christ, which neither diversity of race or customs can diminish, nor trackless wastes of the ocean weaken, nor wars, whether just or unjust, destroy.

Mystici Corporis Christi, para 96