John Gill Commentary 1 Samuel 12:16

"Now therefore stand still and see this great thing, which Jehovah will do before your eyes." — 1 Samuel 12:16 (ASV)

Now therefore stand
Which does not so much respect the position of their bodies as the fixed attention of their minds:

and see this great thing which the Lord will do before your eyes;
meaning the storm of thunder and rain which presently followed; which coming at a time when such things were not usual, and on a day when there was no appearance or likelihood of anything of this kind, and suddenly, at once, upon the prayer of Samuel, it was no less than a miracle, and might be called a "great thing", new and unheard of, and the pure effect of almighty power.