"Literary" Questions

At the moment, I'm reading Tracy Chevalier's "Girl with a Pearl Earring". I find it highly enjoyable to read in the original. It is so much different from translations however no matter how good and professional they are. Especially I'm relishing enjoying the authentic original English language parts that I don't have to no doubt in what they mean. However, there are still questions emerging, e.g. as I continue reading:

1. The first phrase that confused me was: "He was leaning against the threshold". My surprise is that I used to think thought that a threshold is something on the floor. below, I mean can understand how someone can cross the threshold but how can one leaning against it? Is it the same as "to leaning against the doorpost"? Yes.  Look at the 2nd definition: http://www.merriam-webster.com/dictionary/threshold

2. As far as I'm aware the auxiliary verb "shall" isn't really used today but for special cases. At the same time it wasn't for the first time for me to see the following kind of sentence: "I shall have to explain to her." Does it add some particular sense to it when "shall" is used? Actually it's Just a very interesting observation... Yes to your question.  See all the gory details of usage in http://en.wikipedia.org/wiki/Shall_and_will

Thank you!