The Schoolmaster in Theology is Aquinas, who called himself a donkey, an Ass. The other allusion is to Francis of Assisi, or if you really want fun, you can go back to a legend where an Anglo Saxon Saint preached to a cow and donkey.
But it is fun.
I woke and rose and slipt away
To the heathery hills in the morning grey.
In a field where the dew lay cold and deep
I met an ass, new-roused from sleep.
I stroked his nose and I tickled his ears,
And spoke soft words to quiet his fears.
His eyes stared into the eyes of me
And he kissed my hands of his courtesy.
"O big, brown brother out of the waste,
How do thistles for breakfast taste?
"And do you rejoice in the dawn divine
With a heart that is glad no less than mine?
"For, brother, the depth of your gentle eyes
Is strange and mystic as the skies:
"What are the thoughts that grope behind,
Down in the mist of a donkey mind?
"Can it be true, as the wise men tell,
That you are a mask of God as well,
"And, as in us, so in you no less
Speaks the eternal Loveliness,
"And words of the lips that all things know
Among the thoughts of a donkey go?
"However it be, O four-foot brother,
Fair to-day is the earth, our mother.
"God send you peace and delight thereof,
And all green meat of the waste you love,
"And guard you well from violent men
Who'd put you back in the shafts again."
But the ass had far too wise a head
To answer one of the things I said,
So he twitched his fair ears up and down
And turned to nuzzle his shoulder brown.
C. S. Lewis