It's not often that total and utter silence can count as a CMOA, but the reaction by the cast, who have been wrapped up in the commercialism of the season, after Linus gives his sermon is an almost physical entity.
More importantly, when Linus gives his Biblical recitation of the Nativity; it's pure Talking Heads, but its sincerity and dramatic power makes it riveting.
In a meta sense, the sheer staying power of this masterpiece is pretty awesome, especially when you consider that CBS though them special would flop hard. The choppy, sloppy animation has actually become beloved and warmly imitated over the years. Schulz had to fight hard to use child actors instead of adults, which was pretty gutsy considering only three of the kids had any acting experience (The girl who voiced Sally couldn't even read yet!). The CBS execs tried to force Schulz to add a laugh track, but he point-blank refused. He had to lobby hard for the inclusion of Vince Guaraldi's jazz soundtrack over a more traditional one, and the decision to include jazz would be a fateful one (Seriously, can you imagine Peanuts without jazz?). And on top of everything else, the execs were ready to cut the special altogether if Schulz didn't nix Linus's now-iconic recitation of Jesus's Birth from the KJV. Schulz called their bluff and stood firm. In the end, the special payed off in a big way: half of all TV audiences tuned into the first broadcast, the special won a freaking PEABODY award, and it's run for, at this point, 48 straight Christmases. Not bad at all.