Final answer:
Aunt Petunia receives a Howler insisting that she must allow Harry Potter to stay in their home for his safety.
Step-by-step explanation:
The message that Aunt Petunia receives in the Howler after Uncle Vernon tries to kick Harry out pertains to a moment in the Harry Potter series. The Howler insists that Petunia must allow Harry to stay in their home, emphasizing that his safety is paramount due to the protection that their house provides against those who wish to harm him. This incident reinforces the idea that, despite their aversion to magic and Harry's world, the Dursleys are intertwined with Harry's fate, and it underscores the protective measures set in place by the wizarding community to ensure Harry's survival.