What is the significance of this passage from Hamlet?
My father's spirit in arms! All is not well.
I doubt some foul play. Would the night were come!
Till then sit still, my soul. Foul deeds will rise,
Though all the earth o'erwhelm them, to men's eyes.
The former king of Denmark, Hamlet’s father, has appeared as a ghost, an ominous sign in those days. Any spirit could signify that “All is not well,” but a royal specter who is also “in arms,” or dressed in armor, is even more foreboding. Hamlet immediately wonders if there was something unnatural about his father’s death or if there is something else evil afoot. By “doubt,” Hamlet actually means “suspect”: he suspects “some foul play.” He tells his soul to “sit still” because he is no doubt anxious to hear what his father could possibly tell him, wishing that it were night already, the time apparitions are more likely to appear.
Perhaps to calm himself, Hamlet asserts that “Foul deeds will rise, / Though all the earth o'erwhelm them, to men's eyes.” This statement espouses a sense of justice and retribution. No matter how buried or cloaked a wicked act may be, the person who committed that act will eventually be known, via supernatural or natural means. From his meeting with the ghost, Hamlet becomes obsessed with unearthing the truth about his father and uncle. His father’s spirit (or the apparition posing as his father) sets him on an investigative path towards revenge.
This quote from Act I, scene two is said by Hamlet upon hearing from Horatio, Marcellus, and Bernardo of the appearance of a ghost that looks like the dead king. These are Hamlet's final words before the end of the scene, and Hamlet has vowed to wait for the reappearance of the ghost. His words, "All is not well. I doubt some foul play," reveal his suspicions of the king's untimely death.
This speech by Hamlet is significant, because the audience gains understanding that the prince is not satisfied with the new state of events, especially his uncle's marriage to his mother; the idea of "foul deeds will arise" suggests an ominous turn of events to come and Hamlet's hope to find the truth.