to put something into the sound, complete condition it ought to be in: to mend, restore, prepare, or fully equip
TranslatabilityPartialCertaintyStrong
This verb pictures taking something and bringing it to the finished, working, fit-for-purpose state it was meant to have. The underlying idea is not adding a decoration but supplying whatever is missing or out of place so the thing is now whole and ready. That one idea stretches across a wide field of English words because the object changes: a torn net is put back in working order, a person who has slipped is brought back to a sound footing, a body or a world is fashioned and made ready, and a believer's faith is filled out to maturity.
Because the same verb covers such different objects, English translations rotate through a whole set of renderings for it:
"mending" the fishing nets that James and John handled
"restore" someone caught in a fault, gently setting them right again
"prepared" a body, or "framed" the worlds, calling them into their intended form
"perfect" or "equip" believers, completing what is still lacking in them
What holds these together is the single movement from incomplete or disordered to complete and in order. Related Greek τελειόω reaches for the same finish line from a different angle, stressing the goal reached rather than the parts fitted together.
Nuances
1ato mend or repair: put a damaged object back into working order
TranslatabilityDirect
Mat 4:21Mrk 1:19
1bto restore or make whole: bring a person back to a sound condition, or knit a divided group into unity
1Co 1:102Co 13:11Gal 6:11Pe 5:10
1cto prepare, fashion, or bring into being: make something ready or call it into its intended form for a purpose
Mat 21:16Rom 9:22*Heb 10:5Heb 11:3
1dto make complete or equip: supply what is lacking and bring to full maturity or fitness
names being brought to a complete, well-ordered, fully-equipped condition rather than moral flawlessnessLuk 6:40Heb 13:21
Both
both point to a whole, complete state that lacks nothing1Co 1:101Th 3:10
Only perfect
the English word "perfect" suggests absolute or moral flawlessness, a shade the Greek does not require
“mend”
Comparison data is not available for this English gloss yet.
“restore”
Comparison data is not available for this English gloss yet.
“prepare”
Comparison data is not available for this English gloss yet.
“frame”
Comparison data is not available for this English gloss yet.
“equip”
Comparison data is not available for this English gloss yet.
How katartizō differs from similar Greek words
τελειόωτελειόω stresses reaching the goal or intended end, bringing something to completion; καταρτίζω stresses fitting the parts into their proper, sound order so the whole works as it should.
Reaches back before anything was damaged, describing God making something ready that never existed in the first place: the worlds formed at his word, and a body prepared for the Son.Heb 11:3Heb 10:5
Is the ordinary word for working on equipment until it is fit for the job, used of fishermen readying their nets in the boat.Mat 4:21Mrk 1:19
Describes bringing people all the way to maturity and to a working unity, whether that is a student finished with training, a divided church joined in one mind, or believers supplied with what their faith still lacks.Luk 6:401Co 1:101Th 3:10
Both
Both describe putting right what has gone wrong, so that a person or thing works as it should again, which is why English Bibles reach for "restore" with either word.Mrk 3:5Gal 6:1
Both name a finished, settled condition that God himself brings about, whether the promised putting right of all things or the God of all grace steadying his people after they have suffered.Mat 17:111Pe 5:10Heb 13:21
Always looks back to an earlier, proper condition that had been lost, and gives it back: a shriveled hand becomes as sound as the other one again, and a blind man sees again.Mat 12:13Luk 6:10Mrk 8:25
Carries the national and end-time hope of getting back what was taken away, as when the disciples ask whether the kingdom is now being given back to Israel, or when Elijah is promised as the one who puts everything back the way it should be.Act 1:6Mat 17:11Mrk 9:12
Can mean simply giving a person back to the people he came from, with no repair or improvement in view: the writer asks for prayer that he may be returned to his readers sooner.Heb 13:19
katartizō in the other biblical languages
כּוּןHebrew“to establish: establish”כּוּן is the Hebrew verb for establishing, making firm, and setting in place or preparing, which the Greek Old Testament often rendered with this word.
Covers repair, not just completion: fishermen bent over torn nets, putting them back into working shape before the next catch.Mat 4:21Mrk 1:19
Works on people rather than objects, whether gently setting right someone who has slipped or steadying a believer again after suffering.Gal 6:11Pe 5:10
Reaches inside a person or a group: a divided church knit back into one mind, and a student finished off until he is like his teacher.1Co 1:10Luk 6:402Co 13:11
Describes God getting something ready ahead of time for the purpose he intends, whether a body made ready for his Son or containers already shaped for their end.Heb 10:5Rom 9:22
Both
Both name the moment a work under construction stands fully put together, with the Aramaic word used of the finished temple and the Greek word of the world itself assembled at God's command.Ezr 6:14Heb 11:3
Both look at what is still missing and speak of filling it in until nothing is lacking, whether unfinished walls or an unfinished faith.Ezr 4:121Th 3:10
Both are commonly rendered "complete" or "finish" in English, which is why the Greek verb is the natural counterpart when the Aramaic one is put into Greek.Ezr 5:9Heb 13:21
Belongs to one project only: the temple and the city walls in Jerusalem, always a physical structure brought to its finished state.Ezr 5:11Ezr 6:14Ezr 4:12
Lives in official letters and interrogations, where the whole question is who authorized the builders to finish the work at all.Ezr 5:3Ezr 5:9
The finishing itself is the political turning point: opponents warn the empire that once the walls are done the province will stop paying its taxes.Ezr 4:13Ezr 4:16
What scholars say about katartizō
The verb belongs to the ἄρτιος word group ("fitted, complete"), and its basic force is to put something into a fully fitted, functional state. Classical and Hellenistic usage runs from repairing and refitting (nets, ships) to the medical setting of a dislocated bone, and figuratively to ordering and equipping. Standard lexica (BDAG, LSJ) group the New Testament occurrences into two broad domains: putting in order or restoring (nets, an erring believer, a divided congregation) and preparing, creating, or equipping (the created worlds, a body, vessels, believers made mature). Delling's treatment in TDNT emphasizes the same span from restoration to bringing to completion. At Romans 9:22 the participle rendered "fitted for destruction" is grammatically ambiguous between a passive sense (they were prepared) and a middle sense (they prepared themselves), a long-standing exegetical crux with theological stakes that does not, however, unsettle the lexical meaning of the verb itself.
Sources
BDAG, s.v. καταρτίζωlexicon
LSJ, s.v. καταρτίζωlexicon
G. Delling, "ἄρτιος, καταρτίζω, κατάρτισις, καταρτισμός," TDNT 1:475-476dictionary