For the priest's
kohen  (ko-hane')
literally, one officiating, a priest; also (by courtesy) an acting priest (although a layman) -- chief ruler, own, priest, prince, principal officer.
saphah  (saw-faw')
the lip (as a natural boundary); by implication, language; by analogy, a margin (of a vessel, water, cloth, etc.)
should keep
shamar  (shaw-mar')
to hedge about (as with thorns), i.e. guard; generally, to protect, attend to, etc.
da`ath  (dah'-ath)
knowledge -- cunning, (ig-)norantly, know(-ledge), (un-)awares (wittingly).
and they should seek
baqash  (baw-kash')
to search out (by any method, specifically in worship or prayer); by implication, to strive after
the law
towrah  (to-raw')
a precept or statute, especially the Decalogue or Pentateuch -- law.
at his mouth
peh  (peh)
the mouth (as the means of blowing), whether literal or figurative (particularly speech); specifically edge, portion or side; adverbially (with preposition) according to
for he is the messenger
mal'ak  (mal-awk')
a messenger; specifically, of God, i.e. an angel (also a prophet, priest or teacher) -- ambassador, angel, king, messenger.
of the LORD
Yhovah  (yeh-ho-vaw')
(the) self-Existent or Eternal; Jehovah, Jewish national name of God -- Jehovah, the Lord.
of hosts
tsaba'  (tsaw-baw')
a mass of persons (or figuratively, things), especially reg. organized for war (an army); by implication, a campaign, literally or figuratively (specifically, hardship, worship)