From  Understanding Plato: The Smart Student's Guide to the Socratic Dialogues and the Republic

EUTHYPHRO: EXAMPLES OF SOCRATIC METHOD

Part 4 

Piety is not a Skill

After a bit of floundering about, Euthyphro finally hits on another, final definition of piety (D4).  It is “some sort of knowledge of sacrificing and praying” (14c).  The pious person is one who knows how to ask from the gods (prayer) and how to give to them (sacrifice). 

Socrates points out that knowledge of how to give must imply knowing about what the recipient of the gift needs.   This in turn implies that there is some benefit the gods get from the gifts they receive from us.  When Socrates asks, “what could those gifts of ours to the gods possibly be?” Euthyphro replies “honor and reverence and…what’s pleasing to them” (15a).   

 But Socrates points out that this takes us full circle!  For that which is pleasing to them is the same as what is loved by them (R4).  As Socrates puts it “So, once again, it seems, the pious is what’s loved by the gods” (15b), and Euthyphro is back to where he started.  In this case, the elenchus is displayed when Socrates shows Euthyphro that D4 assumes the previously discarded claim in D2 that piety is what all the gods love. 

Socrates now asks Euthyphro “to examine again from the beginning what the pious is,” but Euthyphro has had enough.  “Some other time, Socrates.  You see, I’m in a hurry to get somewhere, and it is time to be off” (15e).