The phrase "My words fly up, my thoughts remain below: Words without thoughts never to heaven go" is from the play "Hamlet." It takes place in Act 3, Scene 3.
During the scene in Hamlet, the king tells Rosencrantz and Guildenstern to go to England with Hamlet. It is after a prayer that the king recites when the line is uttered upon rising. This quote is an example of irony, as the king wasn't meaning the words that he was saying in the prayer. King Claudius believes words without meaning do not reach heaven, and so this quote explains that his words are invalid.
These lines come after Claudius has been trying to pray after he sees the play "The Mousetrap." What he doesn't know is that Hamlet sees him praying and almost kills him