After a lengthy description of the background events, the narrative takes a moment to reset the prophetic sequence. The preceding account goes into great detail about the unfolding situation, specifically describing how Zephaniah read the letter aloud to the prophet. Because of this extended focus on the backstory, attention must be drawn back to the main point.
To achieve this, the text uses a familiar introductory statement to renew the flow of prophecy. This stylistic choice acts as a bridge, tying the previous events together and shifting the focus back to the direct message being delivered by God [מצודת דוד].