Logic is looking for, finding, codifying and applying deductive reasoning to make decisions based on evidence that you believe will be backed by facts, science and math.
It is logical to think that atmospheric conditions precipitate rain.
It is illogical to think ,it rains when "The Gods decide to make rain" .
The difference being, man has evidence of the cycle of water going into the air and then condensing out of the air into droplets. Whereas, there is no evidence that "Gods" exist.
Reasoning based on "logic" doesn't always depend on actually knowing the reason for something but assuming underlying principles will still apply. You can logically assume rainbows have a scientific explanation without being able to describe that reason.
If you claim something is going to have a logical explanation it is a leap of faith in facts. Facts are facts. So if you claim lightning is made by arch angel wings coming together you are being illogical. If you say it's probably electricity you are trying to be logical.