An allusion to Matthew 22:

16 And they sent out unto him their disciples with the Herodians, saying, Master, we know that thou art true, and teachest the way of God in truth, neither carest thou for any man: for thou regardest not the person of men.
17 Tell us therefore, What thinkest thou? Is it lawful to give tribute unto Caesar, or not?
18 But Jesus perceived their wickedness, and said, Why tempt ye me, ye hypocrites?
19 Shew me the tribute money. And they brought unto him a penny.
20 And he saith unto them, Whose is this image and superscription?
21 They say unto him, Caesar's. Then saith he unto them, Render therefore unto Caesar the things which are Caesar's; and unto God the things that are God's.
22 When they had heard these words, they marvelled, and left him, and went their way.