John Wesley on Deuteronomy 33:25

Iron and brass - The mines of iron and copper, which were in their portion, whence Sidon their neighbor was famous among the Heathens for its plenty of brass, and Sarepta is thought to have its name from the brass and iron which were melted there in great quantity. Thy strength shall be - Thy strength shall not be diminished with age, but thou shalt have the vigor of youth even in thine old age: thy tribe shalt grow stronger and stronger.