From his work De officiis ministrorum (Book II, Chapter II), which adapts, fairly radically, the Ciceronian approach to ethics to Christian ethics:
The philosophers have made a happy life to depend, either (as Hieronymus) on freedom from pain, or (as Herillus) on knowledge. For Herillus, hearing knowledge very highly praised by Aristotle and Theophrastus, made it alone to be the chief good, when they really praised it as a good thing, not as the only good; others, as Epicurus, have called pleasure such; others, as Callipho, and after him Diodorus, understood it in such a way as to make a virtuous life go in union, the one with pleasure, the other with freedom from pain, since a happy life could not exist without it. Zeno, the Stoic, thought the highest and only good existed in a virtuous life. But Aristotle and Theophrastus and the other Peripatetics maintained that a happy life consisted in virtue, that is, in a virtuous life, but that its happiness was made complete by the advantages of the body and other external good things.
But the sacred Scriptures say that eternal life rests on a knowledge of divine things and on the fruit of good works. The Gospel bears witness to both these statements. For the Lord Jesus spoke thus of knowledge: “This is eternal life, to know Thee, the only true God, and Jesus Christ Whom Thou hast sent.” About works He gives this answer: “Every one that hath forsaken house, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for My Name’s sake, shall receive an hundred-fold, and shall inherit everlasting life.”
Faith, then, has [the promise of] eternal life, for it is a good foundation. Good works, too, have the same, for an upright man is tested by his words and acts. For if a man is always busy talking and yet is slow to act, he shows by his acts how worthless his knowledge is: besides it is much worse to know what one ought to do, and yet not to do what one has learnt should be done. On the other hand, to be active in good works and unfaithful at heart is as idle as though one wanted to raise a beautiful and lofty dome upon a bad foundation. The higher one builds, the greater is the fall; for without the protection of faith good works cannot stand. A treacherous anchorage in a harbour perforates a ship, and a sandy bottom quickly gives way and cannot bear the weight of the building placed upon it. There then will be found the fulness of reward, where the virtues are perfect, and where there is a reasonable agreement between words and acts.
One of Ambrose's hagiographical symbols is a beehive (he is also patron saint of practically anything bee-related). According to the story, when Ambrose was a baby, he was suddenly surrounded by a swarm of bees. After he was rescued, he turned out to be completely unharmed, indeed, unaffected in any way, except for a drop of nectar or honey on his cheek. His family is said to have regarded it as an omen that he would be an eloquent orator. It's a good emblem for Ambrose's life during the Arian swarm.