What can you learn about Jefferson by the words he chose to use?
While writing the Declaration, Jefferson used many words that were not in the everyday vocabulary of typical American colonists (an example is the word inviolable).
We can learn at least three things from the words that Jefferson chose to use in the Declaration of Independence.
First, we can learn that he was an educated man. The example you give in your explanation shows this. Educated people tend to use a vocabulary that is different from that of uneducated people. The use of words like "inviolable" shows that he was educated.
Second, we can learn that he felt that he was writing for a formal purpose. The Declaration is not written in everyday language because it is not an everyday document. Jefferson had a sense of the importance of the document and therefore used formal language. This tells us he was a writer with a sense for how to use different language for different occasions.
Finally, we can learn that he was a man of the Enlightenment. The phrase "life, liberty, and the pursuit of happiness," for example, comes almost straight from John Locke. Locke was a major Enlightenment thinker. By choosing to use Locke's words and ideas, Jefferson showed that he was a believer in ideas of the Enlightenment.
Beyond the above mentioned aspects about Jefferson, his diction in the Declaration of Independence reveals him to a consummate perfectionist; his word choice is so incredibly deliberate and exacting. He truly felt the burden of what he was trying to create and took the time to choose his words carefully, so that no single word was out of place or might be misconstrued.
Jefferson really was not a great orator, but he was a prolific letter writer, and The Declaration of Independence illustrates his depth of vocabulary and sense of style; the document is imbued with examples of cadence, alliteration, and crisp use of consonants, all of which empower his message.