en_tn_condensed/mrk/10/40.md

But who is to sit at my right hand ... is not mine to give

"But I am not the one who allows people to sit at my right hand or my left hand"

but it is for those for whom it has been prepared

"but those places are for those for whom they have been prepared." The word "it" refers to the places to his right hand and to his left hand.

it has been prepared

This can be stated in active form. Alternate translation: "God has prepared it" or "God has prepared them" (See: rc://en/ta/man/translate/figs-activepassive)