Matthew 17:10-12 why then do the Scribes say, that Elias must first come?

Mace⁽ⁱ⁾ ¹⁰ why then do the Scribes say, that Elias must first come? ¹¹ Jesus answered, 'tis true, Elias was to come first and set all things right. ¹² but I tell you, that Elias is already come, tho' they knew him not, but treated him in an arbitrary manner; with such usage as the son of man shall likewise suffer at their hands.