he cannot bend his back (40).
Colonel Shaw fought so hard and long during the war that he's physically wasted. He sacrificed his body. While his posture is upright and seemingly confident, try tying your shoes without bending your back. Not easy, folks.
frayed flagsquilt the graveyards of the Grand Army of the Republic. (43–44)
The flags are symbols of the soldiers' sacrifice (although they are frayed and fading). We could probably think of a few more comforting things than frayed flags for quilts (like an actual quilt, for one). It seems like even though the sacrifice was great, the reward is little.
Shaw's father wanted no monument (49)
Colonel Shaw's father believed that sacrifice was his son's duty, and that there needn't be a monument to recognize that. Talk about tough love, pops.