Why the imperfect?

Imperfect forms of λέγω characteristically are used either to introduce an initial speech that is more of a monologue than a dialogue or to record the responses of multiple groups to one thing.35 They can also be used in the expected imperfective sense of ongoing or repeated events.—Steven E. Runge, Discourse Grammar of the Greek New Testament: A Practical Introduction for Teaching and Exegesis (Bellingham, WA: Lexham Press, 2010), 159.