We can understand this as Hamlet just wishing that his own body would just melt away. He wishes that his flesh would melt or dissolve away, as a way to escape the corruption and moral decay he sees around him. This quote reveals the grief that has been tormenting his mind, how he wishes to die but is unable to do so as it is a sin to commit such a thing in Christian terms. He feels disillusioned with the world, and overall his desire to kill himself is a prime example of a dispute within himself.