The car rolled down the hill, over the lawn, and into the swimming pool. Pushing a pen or pencil, pounding a typewriter, or punching a word processor just does not appeal to me. When parallel elements are not presented in parallel grammatical form, the result can be awkward and even difficult to follow. Using the previous examples, write two sentences of your own that include a series of parallel phrases. The more nearly parallel the two structures are, the stronger the connection between the ideas will be.
Parallel structures are especially appropriate when two ideas are being compared or contrasted.
History became popular, and historians became alarmed. Will Durant We die. That may be the meaning of life. But we do language. That may be the measure of our lives.