I looked it up, so now I know what Sweatin’ to the Oldies is, and I already knew Richard Simmons enough not to be mystified by the whole thing, but there’s one question my googling has not answered so far: why, in that one episode of the Simpsons, does Ned Flanders thank the lord for SttO volumes 1, 2 and 4? Is there something… fishy… about volume 3? Or is it just some random bit of absurd humour?
Just random silliness. I love how on the audio commentary, Mike Reiss (?) cracks up laughing and asks “What was wrong with volume 3?”
Don’t overthink it. It’s just supposed to make you laugh as you wonder why he didn’t like number three. Flanders liked volumes one, two, and four so much that he thanks God for them before going into surgery, but something about the third one upset him. It’s best left to your imagination.
What I love about the commentary for that episode is Mike Reiss’ story about consulting with his father (a doctor) about the story so they could get some advice. He says he told his father they were going to give Homer a heart attack, and his response was something like “Oh dear God, that’s horrible!” Seems he didn’t think it was very funny for a father of three to have a heart attack at age 36. 
That’s what I thought, but I just wanted to be sure. Thanks!
Here’s the tracklist for Sweatin’ to the Oldies 3. Maybe Flanders believes all those rumors about the lyrics to Louie Louie.