פירוש על מגילה 51:21

If they sold...: One elevates in sanctity and does not downgrade."one elevates in sanctity" as it is written: "Moses set up the Tabernacle" (Shemot 40:18) - Bezalel made it and Moses who was greater than he set it up. "...and doesn't downgrade" as it is written: "...the firepans of those who sinned at the cost of their lives and let them be made into hammered sheets as plating for the altar - for once they have been used for offering to the Lord, the have become sacred..." (Bemidbar 17:3). Because they were sanctified they (remained) sanctified.

because the town square is not normally used for prayer it does not attain any sanctity therefore if you sell the town square the proceeds may be used for anything

there name wasn’t copper-finer but really their occupation was to refine copper