And he made the mercy seat of pure gold: two cubits and a half was the length thereof, and one cubit and a half the breadth thereof.
Why does Moses repeat these detailed instructions twice over when he could have said it once and left it at that? Because Israel needed to hear these sacred things again and again, just as Christ's story is told by four evangelists for the same reason: what matters most bears repeating. And Moses shows his faithfulness by laying the copy beside the original so every reader can see they match exactly.
AI summary
Commenting on Exodus 37:1-9
made the mercy seat of pure gold--To construct a figure, whether the body of a beast or a man, with two extended wings, measuring from two to three feet from tip to tip, with the hammer, out of a solid piece of gold, was what few, if any, artisans of the present day could accomplish.
He made the mercy-seat - See this described Exo 25:17 (note).