Theophylact of Ohrid

But the preaching of it has been spread far and wide over the earth, and increased so, that the birds of heaven, that is, contemplative men, sublime in understanding and knowledge, dwell under it. For how many wise men among the Gentiles, quitting their wisdom, have found rest in the preaching of the Gospel! Its preaching then is greater than all. Again, it put forth great boughs, for the Apostles were divided off as the boughs of a tree, some to Rome, some to India, some to other parts of the world.

Catena Aurea by Aquinas ↗

Augustine of Hippo

In the same manner, then, the catholicity of our mother becomes palpable when others who are not her sons make war on her. It is a fact that this little branch of worshipers in Africa has been broken off from the great tree which embraces the whole world in the spreading of its branches. She is in labor with them in charity, that they may return to the root without which they cannot have true life.

Letter 32 ↗

Ambrose of Milan

Now let us consider the nature of mustard, and the power of comparison. The mustard seed itself is certainly a cheap and simple thing: if it is ground, it releases its strength. Similarly, faith at first seems simple, but if it is tested by adversity, it reveals the grace of its virtue; so that it also fills others who either hear or read with the fragrance of itself. The mustard seed of our martyrs is Felix, Nabor, and Victor: they had the fragrance of faith, but it was hidden. …

Commentary on Luke ↗