Why were shepherds chosen?

I am working on a sermon for Advent this week and have been assigned the passage in Luke 2 where the angel tells the shepherds that Jesus is born and the shepherds leave to go find Mary, Joseph, and baby Jesus.

I did a little research and am a bit perplexed about what I have learned about shepherds. The symbolism of shepherds all throughout the Bible is quite rampant, mostly in thinking about Jesus as the 'Good Shepherd', Psalm 23 of course, and on it goes.

But there were many other shepherds in the Bible. I think of Abel in Genesis 4; Lot and Abram when they separated (they had flocks in Gen 13), and Rachel as a shepherdess when Jacob first sees her (Gen 29). Joseph's brothers were shepherds, which were detestable to the Egyptians (Gen 46), and then of course there is Moses tending to Jethro's sheep when an angel of the LORD speaks to him in the burning bush (Ex 2 and 3). David, a shepherd boy, was chosen as king in 1 Samuel.

Shepherds play an important role in the Bible! Understanding that the common occupation of the day was shepherding and that shepherds were outcasts, were dirty, weren't very honest often times (grazing on other people's land), etc it makes sense that God would choose them to be the first to tell about Jesus being born, right? Luke thinks so and records it in his gospel. Matthew disagrees slightly and records that the Magi came and saw Jesus first.

It is complex to me that God would choose the common, dirty folk to discover and deliver the greatest message ever. The message of hope and of love. He chose ragamuffins and STILL does. The shepherds were doing their work and were receptive to the message. It's so simple and yet so profound.