A.T. Robertson Commentary Hebrews 7:2

"to whom also Abraham divided a tenth part of all (being first, by interpretation, King of righteousness, and then also King of Salem, which is King of peace;" — Hebrews 7:2 (ASV)

A tenth (δεκατην). It was common to offer a tenth of the spoils to the gods. So Abraham recognized Melchizedek as a priest of God.

Divided (εμερισεν). First aorist active of μεριζω, from μερος (portion), to separate into parts. From this point till near the end of verse 3 (the Son of God) is a long parenthesis with ουτος of verse 1 as the subject of μενε (abideth) as the Revised Version punctuates it. Philo had made popular the kind of exegesis used here. The author gives in Greek the meaning of the Hebrew words Melchizedek (King of righteousness, cf. 1:8) and Salem (peace).