I preached on the conversion of Saul last Sunday.
Chris Schlect* points out the phrase, "kick against the goads" has a Greek literature reference. Prometheus was punished by Zeus for giving man fire. He was bound to a rock and an eagle tore out his liver, and every night it would grow back, and be torn out again the next day.
Prometheus does not repent, and is rebuked by Oceanus: "Thou hast not learned humility... Take me for thy teacher, and kick not against the goads, for there rules in heaven an austere monarch who is responsible to none.
Interesting to consider that the well-educated Saul could well have known this story, and that Jesus may have used it to make this point.
*Credenda/Agenda, Vol 7, No. 6, pg. 27