Howard S. answered 07/23/19
From Sage confidently learn to read for meaning and much much more
Main idea and thesis come down to almost but not totally the same thing.
Yes, the thesis definitely embodies a main idea.
At the same time, a thesis should exude more energy and focus than a main idea.
How so?
What does a thesis have that a main idea may not have?
A thesis has an extremely pointed, sharp, emphatic position.
A thesis should contain energetic, vibrant words, especially verbs.
A thesis should act as a frequent emphatic reminder throughout an
entire essay of the main position.
A thesis should emerge extremely concise: no wasted, extra ("fat")
words.