Easier to read, easier to remember, and easier to believe: this sequence is an example of parallelism. With parallelism, “equal” thoughts are expressed in “equal” grammar.

Faulty parallelism is the opposite: equal thoughts are expressed in unequal—or different—grammar. For example:

Using parallelism to make complex ideas easier to read, easier to remember, and also more believable. 

Parallelism happens between sentences as well as within them:

After the Suez debacle, each country drew a major conclusion. The British realized that they would have to defer to the United States. The Israelis realized that only the United States could offer the support they needed. And the French realized that the Americans could not be trusted.

Faulty parallelism:

The British realized that they would have to defer to the United States. The Israelis realized that only the United States could offer the support they needed. And the untrustworthiness of America was the message received by the French.

Parallel structures are easier to read because they’re easier to remember. When we read, each successive structure lingers in memory for a moment, so that when the next structure is the same, we read it more quickly.

Easier-to-read also means easier-to-believe, thanks to the "familiarity effect." Our brains are wired to equate the familiar with the true, so new ideas phrased in parallel structures are more persuasive because they feel more familiar, and thus more true.