Explaining what soap does and why people should value it would be the real challenge. Communication in general would need to be built from scratch. No english, no latin languages, no modern gestures like thumbs up and hand shakes, no common ground.
Depending on the era, I would bet on agriculture and fermentation as my empire-building tech. Wine first, then bread which is a little bit harder. Maybe spices also, I heard some pretty large empires were built on the power of funny flavors.
So, 100,000 years ago you would need to convince people to join you in this crazy agriculture thing without any metal tools.... without domesticated animals either, by the way... as that would still be thousands of years in the future...
Finally, just taking a large amount of food and leaving it for a long time to ferment somewhere well protected, while everyone around is hungry, would be a huge challenge already. You might need to protect it both from people and from very large wild animals that had not gone extinct yet and would love to take that food from you (and likely use you as food also).
I can convince my first followers by doing the first crops and batches myself, alone.
Usage of animals and metal tools in agriculture came much later. I don't need that to start. I just need fire and ceramics.
Of course it wouldn't be _easy_. Empires are never easy.
Ultimately, what I'm saying is the context of the original comment about soap: food tech would be more succesful than soap tech.