Final answer:
The author likely used Grace's recollection to underscore Abraham Lincoln's character as a kind but melancholic leader burdened by the challenges of the Civil War, underscoring his humanity and the significant responsibilities he shouldered.
Step-by-step explanation:
The most likely reason that the author ends the story with Grace's recollection that Abraham Lincoln "seemed so very kind but looked very sad" is to support the characterization of Lincoln as a great man who faced very difficult situations. This narrative choice emphasizes Lincoln's humanity and the weight of the presidency during one of the nation's most tumultuous periods. The description of Lincoln's sadness likely reflects the immense burden he carried in steering the nation through the Civil War and pursuing the path of reconciliation in its aftermath. The inclusion of Grace's perspective on Lincoln's character could also show how much Grace's opinion of Lincoln had changed over time, suggesting that her understanding and appreciation of him deepened, further underscoring his complex leadership during hardship.