Isa. 1:20 KJV (With Strong’s)

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20
But if ye refuse
ma'en (Hebrew #3985)
to refuse
KJV usage: refuse, X utterly.
Pronounce: maw-ane'
Origin: a primitive root
and rebel
marah (Hebrew #4784)
to be (causatively, make) bitter (or unpleasant); (figuratively) to rebel (or resist; causatively, to provoke)
KJV usage: bitter, change, be disobedient, disobey, grievously, provocation, provoke(-ing), (be) rebel (against, -lious).
Pronounce: maw-raw'
Origin: a primitive root
, ye shall be devoured
'akal (Hebrew #398)
to eat (literally or figuratively)
KJV usage: X at all, burn up, consume, devour(-er, up), dine, eat(-er, up), feed (with), food, X freely, X in...wise(-deed, plenty), (lay) meat, X quite.
Pronounce: aw-kal'
Origin: a primitive root
with the sword
chereb (Hebrew #2719)
drought; also a cutting instrument (from its destructive effect), as a knife, sword, or other sharp implement
KJV usage: axe, dagger, knife, mattock, sword, tool.
Pronounce: kheh'-reb
Origin: from 2717
: for the mouth
peh (Hebrew #6310)
the mouth (as the means of blowing), whether literal or figurative (particularly speech); specifically edge, portion or side; adverbially (with preposition) according to
KJV usage: accord(-ing as, -ing to), after, appointment, assent, collar, command(-ment), X eat, edge, end, entry, + file, hole, X in, mind, mouth, part, portion, X (should) say(-ing), sentence, skirt, sound, speech, X spoken, talk, tenor, X to, + two-edged, wish, word.
Pronounce: peh
Origin: from 6284
of the Lord
Yhovah (Hebrew #3068)
(the) self-Existent or Eternal; Jehovah, Jewish national name of God
KJV usage: Jehovah, the Lord. Compare 3050, 3069.
Pronounce: yeh-ho-vaw'
Origin: from 1961
g hath spoken
dabar (Hebrew #1696)
perhaps properly, to arrange; but used figuratively (of words), to speak; rarely (in a destructive sense) to subdue
KJV usage: answer, appoint, bid, command, commune, declare, destroy, give, name, promise, pronounce, rehearse, say, speak, be spokesman, subdue, talk, teach, tell, think, use (entreaties), utter, X well, X work.
Pronounce: daw-bar'
Origin: a primitive root
it.

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Cross References

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if ye refuse.
for the mouth.

J. N. Darby Translation

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20
but if ye refuse and rebel, ye shall be devoured with the sword: for the mouth of Jehovah hath spoken.