Reread Lady Macbeth's soliloquy, lines 35-51 in scene 4 and Duncan’s reaction lines in scene 6. Why does she ask the spirits to fill her with “direst cruelty” and “make thick my blood”? What does this speech reveal about her

Lady Macbeth is asking the spirits to provide her with strength..... the strength she will need to do murder.

In order to preform murder in a manly and stealthy fashion one needs a manly courage (as the convention goes) and Lady Macbeth is asking for the same. She asks for a cold heart and congealed blood so that the sight of blood itself won't send a cold shock to her heart. This reaveals her womanish side and also points out Macbeth's own impotence to carry out the deed himself.