Syntax is how the words are combined in a piece. Pay attention to grammatical structure, as it contributes to the flow and pacing of what is being communicated.
In a periodic sentence, the main idea is withheld until the end, creating tension and interest. (Neat Quick Note: A reader is more likely to remember the last thing they read in any given segment. This is why the thesis goes at the end of your first paragraph, and why a call to action is most effective at the end of an essay.)
In loose sentences, the main idea is presented at the beginning, allowing the reader to closely read the supporting ideas closely (which is why we put the thesis before the supporting argument).
Complex sentences provide a more relaxed pace.
Compound-complex sentences are reflective and distancing.
Syntactical variation is one of the most important skills a writer can learn. In order to hold interest and emphasize important points a writer must understand how a natural voice is replicated in text. There are two ways to do this: Read well and read often; read often and write well.