They were, of course, likely nearby, which means that they could come quickly and see the baby before he moves on in the morning. They were relatively isolated out in their fields, which means that the angel could come to them fairly easily, without being seen by the masses. They were of a lowly state in society, most likely. Notice that the angels did not come to proclaim the birth to the priests or to the tax collectors or to the Roman guard. They didn't come to those who were known, but to those who were unknown, who were just doing what they were supposed to be doing, what they were entrusted to do.
The faithful become the first of the faith.
See, it's a strange thing about shepherds - they're never taking care of their own flocks. The animals sort of become their own the more time they spend together out in the fields, and the animals respond to the voice of the shepherd, but they always belong to someone else. Sometimes, the shepherds were hired hands, servants. They were brought in solely for the task of tending the flocks and keeping them.
Often, however, the shepherds were sons. Think about the Old Testament, when the Lord is ready to anoint David to be King over all Israel. Samuel goes to Jesse, David's father, in search of the selected King and finds no one. When he inquires about another son, there is but one - the one who is out in the field, tending the flocks. The shepherd boy.
The shepherds become the first witnesses to the promised descendant of the shepherd.
The sons (likely) become the first witnesses to the Son of God.
We should also say here that it's quite possible that some of the shepherds may also have been female. We know that when Jacob goes back to his home country to seek a wife, Rachel has brought her father's flocks to the well for a drink and is waiting on the other shepherds to arrive with their flocks. So it's quite possible that some of the first witnesses of the Christ child may have been not sons, but daughters. But I digress.
The shepherds were conveniently located to the manger in Bethlehem, but that's not why God called them to be witnesses. He didn't call them because they were already shepherds and therefore less likely to be offended by the smell of the barn. He didn't call them because they were simple folk and wouldn't think to try to exalt the child before His time. He called them because they were humble folk who could appreciate the sacred moment unfolding before them. He called them to be witnesses because they had so much in common with what was happening in that stable.
And He sent the whole host of angels to call them to come.
We don't have much of a frame of reference for shepherding these days, but this Christmas, there's a lot that we can learn from them as we prepare our own hearts and minds to see.
Perhaps most pressing, we must remember that we are but servants, and we must be faithful servants. What we have here is not our own, though we are called to care for it. Being separated, set apart, we become the voice that our flock knows; we must be the ones our flock trusts. We must be the ones who give our lives for others, who invest all we have in what we are given.
This Advent, let us be faithful. Let us be good stewards of our lives, of our responsibilities, of our opportunities, that we may be called among those who come to see the Faithful One in living flesh. Let us be the kind of servants who give all we have for the sake of the One we serve, that we may be called to come and see the One who will give all He has for our sake.
O come, all ye faithful. Like shepherds from the fields.