"I do, indeed, close my door at times and surrender myself to a book, but only because I can open the door again and see a human face looking at me"

The quote recommends that while the speaker delights in reading, they do not wish to completely isolate themselves from human interaction. They just close their door to check out due to the fact that they know they can go back to interacting with others when they pick to open it once again. This suggests that they see the value of both solitude and social connection.