Thirty-five years ago last week, the world got one hell of a Christmas gift when The Simpsons aired its first full episode, “Simpsons Roasting on an Open Fire.”

Sparking a nearly four-decade television run — and counting! — an ever-quotable movie and a series of predictions so strangely astute they’ve been known to leave even the most adept psychic shaking their fist at the sky, no one knows the extent of The Simpsons’ legacy quite like voice actress Yeardley Smith.

Last Tuesday, Smith — who has played Lisa Simpson throughout the series’ entire run — headed to Instagram with a glimpse at the Disney+ celebration for The Simpson’s latest holiday installment, “O C’mon All Ye Faithful,” a two-part special scheduled to coincide with the series’ long-awaited coral anniversary.

But beyond just hyping the episode — one the actress dubbed an “instant Christmas classic” — Smith took care to offer a few words of...