Or HaChaim on Exodus 37:8/אור החיים על שמות ל״ז:ח׳

1 משני קצותיו, at the two ends thereof. Perhaps the verse wants to inform us that Betzalel did not make the lid of equal thickness throughout before pounding it with a hammer. He may have flattened it with hammer blows to correspond to the size required to fit as a lid over the Ark. He had added additional amounts of gold at either end so that he could fashion the cherubs out of that excess. This is why the Torah had to specify that the cherubs were made from the respective extremities of the lid.