Lyric discussion by twinter 

Cover art for Clara lyrics by Punch Brothers

Frontman Chris Thile sings "Douglas Fir" about five years later. There's a Clara in that song too:

"No sooner does the Fir grow tall In Clara's dream Than we lose our little girl And gain (and gain) a sugar plum fairy"

Clara is a daughter who's already died. He's sining to her. He's not asking her to come back ("Someday don't wake up I want you to get some rest").

But he's talking to her all the same and possibly struggling with suicidal thoughts in the wake of the tragedy.

Bottom line, there's a lot of himself that can't be separated from who he is in relation to her: her father. And there's a lot he wants to tell her regardless of whether he'll make it out of his grief ("It's gonna be a long night... your eyes are not a window, they're a one-way mirror to my soul")

But he still ends with trying to let her go. "I want you to get some rest."

My Interpretation