With the quote, we simply credit the source. The decision to use a quotation should depend in part on your evaluation of the jury, the situation, and more importantly, on an assessment of your ability to pull it off. Quotes or catchy phrases will work on some jurors but not on others. Some cases, e.g. , a plain vanilla one with few emotional overtones, are less conducive to quotes than others. Similarly, some of us appear stilted and insincere when we speak anyone else's language than our own.
Nothing is quite as inane in conversation as bookish language from a person who seems insincere.
Choice of source should also fit the speaker's style. A great danger in using quotations is that there is a natural propensity to overdo it. The defender should never simply wrap himself in quotations of others as a beggar might seek to enfold himself in the purple of an emperor. Too much reliance on the words of others may lead your jury to believe that you are not speaking from the heart. When quotes are used, they should, if possible, be spoken from memory and not read.