Shepherds’ song?

I was reading a Christmas advent devotional today and thinking about the shepherds. I was thinking about how they felt when they saw the angel.

Luke tells us they were terrified. Why?

God had been silent for 400 years. Now he was breaking that silence. For what? To bring judgment on his people?

No. To bring good news.

His anger was ended. And now he was bringing salvation through his Son.

Did the shepherds think of Isaiah 12 when they heard the angels?

Probably not. But if they had, I think they would have been singing it.

I will give thanks to you, Lord,
although you were angry with me.

Your anger has turned away,
and you have comforted me.

Indeed, God is my salvation;
I will trust him and not be afraid,
for the Lord, the Lord himself,
is my strength and my song.
He has become my salvation. (Isaiah 12:1-2)

Jesus, the root of Jesse had come. (Isaiah 11:1-5, 10)

And after seeing Jesus, the shepherds went and told everyone what they had seen and heard. (Luke 2:16-18)

Cry out and sing, citizen of Zion,
for the Holy One of Israel is among you
in his greatness. (Isaiah 12:6)