How is parallelism used here to strengthen the argument

For cutting off our trade with all parts of the world: For imposing taxes on us without our consent: For depriving us in many cases, of the benefits of trial by jury

The use of parallellism makes the reader focus on the message.

Explanation:

The author uses parallellism to emphasize the main reasons why an action has been taken, giving them order and seriousness. The reader will focus on the main message and will percieve the series of justifications more easily, consequently, the author will communicate their ideas and intentions clearly.

The repetition of for followed by negative verbs emphasizes that there is a long list of bad things the king did.