Now therefore stand still and see this great thing, which Yahweh will do before your eyes.
The great miracle here was in the timing of the thunderstorm, which came directly and immediately upon Samuel's praying for it in the presence of all the people.  Such a thing as a rain during the wheat harvest was about as unusual as anything that could have happened, just like snow in July or August!  In fact, the author of Proverbs gives us this: