In his first soliloquy, Hamlet expresses his deep melancholy that pervades all his subsequent speeches:
How weary, stale, flat and unprofitable
Seem to me all the uses of this world!
Fie on't! ah, fie! 'tis an unweeded garden
That grows to seed; things rank and gross in nature
Possess it merely.
After encountering the ghost of his father and learning that he has been murdered, and after recognizing the corruption of the state of Denmark in the hasty marriage of Claudius to his mother, that
With mirth in funeral, and with dirge in marriage,
In equal scale weighing delight and dole,
Taken to wife (1.2.13-15)
Hamlet refuses to accept the conditions of the royal court and becomes so depressed that he contemplates suicide, for he perceives the world as "an unweeded garden," a place in which there is a corruption that has overtaken the state of Denmark. This marriage of his mother to his uncle has disturbed Hamlet enough, but having learned from the ghost of his father that it is his uncle who is the very murderer of King Hamlet, Hamlet feels that his world now is like a garden filled with weeds that are "rank and gross in nature." Or, as Marcellus says later in Scene 4, "something is rotten in the state of Denmark."