In Sermon 105, c. 4-10, St. Augustine elaborates further on the symbolic meaning of the “three opposing” choices of gift in this passage, and he gives the egg a little more credit. Here’s the egg parts from chapters 5-10:
“What’s left is hope — which, it seems to me, is compared to an egg. For hope is for a thing that has not yet arrived; and an egg is something, but it’s not a hen yet.
“And so quadrupeds give birth to children, but birds to a hope of children.
“Therefore, it is for this that hope cheers us on: that we may despise present things and hope for what is to come, forgetting what is behind us, when we are reaching forward along with the Apostle [Paul]. For he says it this way: ‘But one thing I do: I forget what is behind in stretching forward to what is ahead, leaning toward the finish line, to win the palm leaves of the supernal vocation of God in Christ Jesus.’
“Nothing is such an enemy of hope as considering what is behind us — that is, to put hope in those things which cross our path and slip past us….
“Be afraid of the example of Lot’s wife. For she looked behind her, and she stayed where she looked. She was turned into salt; she was pickled in brine as an example for the prudent.
“The Apostle Paul has spoken about this hope, like this: ‘For we are saved by hope. But hope that is seen, is not hope. For why does a man hope for what he sees? But if we hope for that which we do not see, we wait for it with patience.’
“‘For why does a man hope for what he sees?’
“There is an egg. It is an egg, and it is not a hen yet.
“And there is a turtleshell. The turtle is not seen, because it is covered by the shell. With patience, it can be awaited. Let it warm up, and it will come back to life.
“Work toward this finish line: to lean forward, to forget the past. For the things which are seen are temporal things.”
“‘Not looking back,” he says, ‘at what is seen, but considering what is not seen. For the things which are seen are temporal things, but the things which are not seen are eternal.’ (2 Cor. 4:18)
“Therefore, reach out your hope to those things which are not seen. Wait for them! Hold on! Don’t look back!
“Fear the scorpion coming for your egg! See how it strikes with its tail, which it holds behind it.
“Therefore, don’t let the scorpion kill your egg! Don’t let this world kill your hope, I tell you, with the poison that’s behind it, which goes against you!
“How much the world says to you! How much ruckus it makes behind your back! It’s all so you will look back — that is, put your hope in things of the present. But not really of the present — they can’t be said to be things of the present, because they don’t stay that long.
“And it’s so that you will move your hope away from what Christ promised and has not yet given you, but which He will give because He is faithful. It’s so that you will turn your soul away, and wish to quit, still in this dying world.
“…If I have hope, if I hold onto hope, my egg will not be struck by the scorpion.”
“…All those who blaspheme against our Christ because of these adversities — they are the tail of the scorpion.
“Let us put our egg under the wings of this Gospel hen who clucks, ‘Jerusalem, Jerusalem,’ to those false and wandering ones. ‘How often would I have gathered together your children, as the hen gathers her chicks? But you would not.’
“It is not said to us: ‘How often would I’ and ‘You would not.’
“For this Hen is the Divine Wisdom. But He assumes flesh so that He may fit with His chicks.
“Look at the other hen – the one of molting plumage shaking her wings, with a voice broken and quavering and weary, and sluggish to gather her little ones.
“Therefore, let us put our egg — that is, our hope — under the wings of this Hen over here.
“Perhaps you notice how a hen can peck up a scorpion. So therefore, would that this Hen would also peck up and devour these blasphemers, creeping out of their caves and crawling across the earth, and stinging us with evil! Let the Hen drag them into her Body and turn them into eggs!
“…Let them stop blaspheming. Let them learn to adore. Let the stinging scorpions be eaten by the Hen, and be converted by being drawn into the Body! Let them be trained on earth, and crowned in Heaven.”
This is actually topical, as one of the old games with Easter eggs was to knock your egg against that of a neighbor at table, and see which egg was the strongest.