What does Creon remark that is the most important act a son can do?
Creon is big on familial loyalty. He argues that obedience, and (depending on which translation you read) potentially emulation is the duty a son owes his father. Haemon, his son, he argues, should try to be like his father, and try to obey hsi will, and his decisions, regardless of what Haemon himself thinks.
Creon thinks he should be allowed to pick Haemon's ideas, his friends, and even his future wife. Sons of fathers, like subjects of a king, have to obey the man in charge. And Creon, as king and Haemon's father, therefore is due a double dose of loyalty and obedience.
The slight problem with Creon's insistence on familial loyalty is that he himself is foregoing familial privilege by refusing to bury Polyneices, his nephew. He might be doing the right thing as king in forbidding the burial (though the play leaves that ambiguous) but, as the familial guardian, he certainly isn't. One of the key points of this play is that you can't separate politics from family. A man isn't just the king, but also the man.