Jerome
Catena Aurea · Matthäusevangelium 13
Another parable put he forth unto them, saying, The kingdom of heaven is like to a grain of mustard seed, which, a man took, and sowed in his field: Which indeed is the least of all seeds: but when it is grown, it is the greatest among herbs, and becometh a tree, so that the birds of the air come and lodge in the branches thereof.
For the dogmas of Philosophers when they have grown up, shew nothing of life or strength, but watery and insipid they grow into grasses and other greens, which quickly dry up and wither away. Brit the Gospel preaching; though it seem small in its beginning, when sown in the mind of the hearer, or upon the world, comes up not a garden herb, but a tree, so that the birds of the air (which we must suppose to be either the souls of believers or the Powers of God set free from slavery) come and abide in its branches. The branches of the Gospel tree which have grown of the grain of mustard seed, I suppose to signify the various dogmas in which each of the birds (as explained above) takes his rest. Let us then take the wings of the dove, that flying aloft we may dwell in the branches of this tree, and may make ourselves nests of doctrines, and soaring above earthly things may hasten towards heavenly. (Ps. 55:6.)