The priest’s office (tēn hierateian). lxx and Koiné word from hiereus, in N.T. only here and Luk 1:9.
To take tithes (apodekatoin). Present active infinitive (in -oin, not -oun, as the best MSS. give it) of apodekatoō a lxx word (apo, dekatoō), to take a tenth from (apo).
Brethren (adelphous). Accusative case in apposition with laon (people) unaffected by the explanatory phrase tout' estin (that is).
Though come out (kaiper exelēluthotas). Concessive participle (cf. Heb 5:8) with kaiper (perfect active of exerchomai).