Litotes is a figure of speech in which the speaker expresses a strong positive meaning by using two negative words or a negative word with a word that means the opposite of the meaning he intends. A few examples of negative words are "no," "not," "none," and "never." The opposite of "good" is "bad." Someone could say that something is "not bad" to mean that it is extremely good.
Some languages do not use litotes. People who speak those languages might not understand that a statement using litotes actually strengthens the positive meaning. Instead, they might think that it weakens or even cancels the positive meaning.
By using litotes, Luke emphasized that there was a <u>lot of excitement or anxiety</u> among the soldiers about what happened to Peter. (Peter had been in prison, and even though there were soldiers guarding him, he escaped when an angel let him out. So they were very agitated.)