When God told Moses that every counted Israelite must give a half-shekel, Moses did not know what a half-shekel looked like. The coin did not yet exist in any earthly mint. So, Targum Pseudo-Jonathan preserves a tradition: God showed him one. On Mount Sinai, a coin of fire appeared — a denarius of fire — hovering before his eyes, glowing with the weight and image it would bear when struck in silver (Exodus 30:13).
This is one of the most striking targumic expansions in all of Exodus. The classical midrashim (Tanchuma Ki Tisa and Bamidbar Rabbah preserve variants from the 5th-8th centuries CE) record that Moses was shown three things he could not otherwise imagine: the menorah of pure gold, the red heifer, and the half-shekel coin. Each of these required God to reach down into the material world and hand Moses a flaming prototype.
Why fire?
Because the half-shekel was no ordinary coin. It was the ransom for a soul — a spiritual currency first, a piece of silver second. Moses needed to see it in its true element before he could translate it into metal. Fire was the sign that this was a heavenly object temporarily taking physical form. The image remained with him when it faded. The silversmiths could strike what Moses remembered.
The targum specifies the weight — twenty manin, the standard of the sanctuary — and the purpose: a separation before the Lord. Every coin was an act of setting aside, a person declaring, "This much of me belongs to something larger."
The Maggid learns: sometimes you cannot describe what God wants from you. It has no earthly model. You have to be shown it in fire first, and then carry the memory into the world and mint it, coin by coin, from whatever silver you have.