Synthesis refers to the output of the task. For eg. if you take chemical substances, the reaction of chemical substances refers to “Synthesis”.
Synthesis in terms of post-reading, the word refers to one of the phase in the reading process where the content which is read are to be connected to what we know already and what we learnt newly. It is the outcome of reading.
There is one another term called “stimulation” which refers to the overall design of the reading.
The purposes of the two passages are different. The first passage is biographical and contains quotes that reflect Grady's feelings about Reconstruction. The second passage is a personal essay which directly states the author's feelings about Reconstruction.
Most research papers begin with a thesis statement at the end of an introductory paragraph. Even if it’s not a requirement, it’s a good idea to write a thesis statement as you begin to organize your research.
I think the single sentence that shows it is a personal letter is "that all I can say is that I am well" as the rest of the letter is details about his military campaign so could be part of a more formal memo if it were not for this opening sentence so that seems to be how to identify it as such.
