Themes in Machiavelli's The Mandrake include:
1) Deception is a valid option if it achieves positive or favored results. This is by far, the main theme of the play. In the story, Callimaco lusts after another man's wife. Callimaco wants to bed Lucrezia badly. Unfortunately for Callimaco, Lucrezia is not only beautiful but quite the virtuous soul; she would never willingly sleep with another man. He enlists the aid of one Ligurio, a shrewd but dishonest marriage broker. Callimaco is willing to try anything
...even if it is grandiose, or dangerous, or harmful, or infamous. It’s better to die than to live like this...
Both convince the gullible Nicia that the remedy for Lucrezia's supposed infertility is the mandragola. Callimaco, disguised as a doctor, tells Nicia that if it weren't for the mandragola, any number of French princesses and even the Queen of France would be barren. However, he also warns Nicia that the first man to sleep with Lucrezia after she has ingested the potion would die within a week. The remedy, of course, is to get some other man to do the first honors: to draw out the poison before Nicia beds his wife. However, Nicia balks at this because he doesn't want to be a cuckold, nor does he want to make his wife a whore. Callimaco assures him that princes, kings, and lords have all taken this path, insinuating that Nicia would be a fool not to do so if his desire is to have an heir.
Callimaco proposes kidnapping some random man off the street to sleep with Lucrezia. By this time, the foolish Nicia is warming to the plan. However, he is skeptical that his virtuous wife would agree to such an undertaking. Ligurio suggests taking Lucrezia to her confessor, but Callimaco pretends to be doubtful this course would be successful. Ligurio assures everyone that they have three things in their favor: money, their persuasive powers, and the known corruption of priests. Ligurio further suggests taking Lucrezia's mother along for further reinforcement. After all, Ligurio reasons that 'her mother thinks the way we do.'
Here, we can see that everyone is willing to engage in some manner of deception in order to bring about a desired result: Nicia gets an heir, Lucrezia gets to be a mother, Lucrezia's mother gets a grandchild, Callimaco gets to bed the beautiful Lucrezia, Ligurio gets some monetary profit out of the deal, and Friar Timoteo gets his share of the cash.
2) Corruption is often hidden in the guise of religion.
Ligurio tells the priest a made-up story about a girl who becomes pregnant out of wedlock. She is supposedly from a good family, and her parents want to cover up the shame of the pregnancy. Accordingly, she lives in a nunnery, and Ligurio suggests that the nuns have either been inept in discharging their duties to their charge, or the girl has a headstrong personality. Either way, Ligurio wants Friar Timoteo to persuade the abbess of the convent to convince the girl to ingest a potion that will abort the baby. Ligurio sweetens the deal with the offer of three hundred ducats. He slyly tells the friar that he could be the one to distribute the money as alms to the poor.
The corrupt priest readily agrees. However, Ligurio later tells Friar Timoteo that the girl has miscarried. The priest pretends to be indignant (he knows the story was made-up anyway). Ligurio states that all is not lost if only the priest would do them another favor: to win the three hundred ducats, he has to convince Lucrezia to drink the mandragola potion and sleep with Callimaco.
Again, the priest has no problems with this because he suspects the truth of the matter.
This rogue Ligurio came to me here with that first tale to test me, so that if I agreed to that he could lead me more easily to this...The fact is that I have been deceived, but the deception is to my advantage.
The priest twists the Scriptures to support his craven ambition:
As for whether the act is a sin, that is easy: because it is the will that sins, not the body...
The Bible says that the daughters of Lot, thinking that they were the last women in the world, lay with their father, and because their intention was good, they did not sin.
Here, it can be seen that the priest is willing to gamble the salvation and happiness of his constituents for financial gain. To that end, he is a true devotee to Machiavellian principles.
And often people get into much trouble for being too obliging and too nice, as for being too mean. God knows I didn't intend any harm...But I console myself with this, when something matters to a lot of people, a lot of people take care.
Hope this helps! Thanks for the question.