Explain the meaning of the following quotation: “Each day mankind and the claims of mankind slipped farther from him. Deep in the forest a call was sounding, and as often as he heard this call, mysteriously thrilling and luring, he felt compelled to turn his back upon the fire, and to plunge into the forest…But as often as he gained the soft unbroken earth and the green shade, the love of John Thornton drew him back to the fire again