to make clean: to remove what defiles a body, an object, or a person
TranslatabilityPartialCertaintySettled
This word covers the whole act of making something clean by taking away whatever spoils it. In the Gospels it is what Jesus does to people with a dreaded skin disease: he makes them clean, healing the illness and restoring them to normal life among others.
The same word carries over to the world of religious purity, where being clean or unclean was a matter of standing before God. Here it can mean scrubbing a cup, or a formal declaration that a food or a person now counts as clean and may be approached without defilement.
Its deepest use in the New Testament is moral and spiritual: cleansing a heart, a conscience, or a whole people from sin and guilt. This is not a separate word but the same picture applied inward. Just as disease and ritual stain had to be washed away before a person could rejoin the community or the worship of God, sin is pictured as a defilement that must be removed before a person can stand clean before God. The three uses share one core idea: something that spoils is taken away so that what remains is fit and acceptable.
Nuances
1ato heal and restore someone from a defiling skin disease
Used for physical healing that removes defiling disease, above all the cleansing of those with leprosy so they are fit to rejoin the community.Mat 8:3Mrk 1:42Luk 5:13Luk 17:14
Names the removal of dirt or impurity from an object or from food, scrubbing the outside of a cup or declaring foods no longer unclean.Mat 23:25Mat 23:26Mrk 7:19Act 10:15
Points to God's decisive cleansing from sin and guilt, wiping away defilement through the blood of Christ or by faith.Eph 5:26Tit 2:14Heb 9:141Jn 1:71Jn 1:9
Both
Both call for making a person clean and fit to draw near to God, and are set side by side as the response to a divided, sin-stained life.Jas 4:8
Names the ritual act of making oneself ceremonially ready to approach God, the formal purification a worshiper undergoes before worship or a vow.Jhn 11:55Act 21:24Act 21:26Act 24:18
Reaches into the inner life as a moral discipline the person takes up, purifying the heart or oneself in hope and obedience.1Pe 1:221Jn 3:3
removes defilement to make a person or thing clean, the standard word for a leper being pronounced clean and for God declaring foods clean, not the curing of an illness as suchMat 8:3Mrk 7:19Act 10:15
extends to moral and inward purity: scrubbing the inside of the cup, cleansing the conscience, and washing the believer clean from sinMat 23:26Heb 9:141Jn 1:7
Both
both can describe the single act that makes a sufferer whole again, so the leper Jesus restores is called cleansed and in the same episode is said to be healedLuk 17:14Luk 17:15
names the curing of a physical ailment, restoring a sick or injured body to health (a servant's paralysis, a fever, a severed ear), where the trouble is sickness rather than defilementMat 8:13Act 9:34Luk 22:51
reaches beyond the body to spiritual restoration: the forgiven or turned-back person is said to be healed, and healing stands for God mending a wounded peopleMat 13:15Jas 5:161Pe 2:24
katharizō in the other biblical languages
טָהֵרHebrew“be pure”the main Hebrew verb for being or becoming clean in the purity laws, which the Greek Old Testament regularly renders with this word
Names an active cleansing of the heart and conscience, an inward washing before God that goes beyond outward condition.1Jn 1:71Jn 1:9Heb 9:14
Used when Jesus overturns the old boundary between clean and unclean, declaring foods and people clean that the priestly system had kept apart.Mrk 7:19Act 10:15Act 11:9
Both
Both name the cleansing of a person from a skin disease, the healing that restores them to normal life.Lev 14:7Mat 8:3Mrk 1:42
The Greek word is the standard counterpart of the Hebrew: both cover the move from unclean to clean, whether the defilement is physical or moral.Lev 17:152Co 7:1
The everyday word of the priestly system for the state of being ritually clean, and for the moment a person is pronounced clean after a prescribed rite.Lev 13:6Lev 14:8Num 19:12
Frames cleanness as the fitness to approach God once defilement is removed, most solemnly on the day the whole nation is made clean before him.Lev 16:30Lev 16:19
Cleansing a diseased body, above all the healing of leprosy pronounced as a verdict of cleanness. This is a physical-restoration sense that the Hebrew word never carries.Mat 8:3Mrk 1:42Luk 17:14
Declaring foods or things ceremonially clean, lifting the clean-versus-unclean boundary. The Hebrew word has no such declaratory sense.Mrk 7:19Act 10:15Act 11:9
Both
Both describe making or keeping a person morally pure before God.2Sa 22:271Jn 1:9
Both denote purifying in a worship setting, the cleanness required of those who handle holy things. The Greek word is a standard rendering for this cultic-purity sense.Isa 52:11Heb 9:22
To pick out or choose, to single out the chosen ones for a task. This selecting sense is entirely absent from the Greek word.1Ch 7:401Ch 9:221Ch 16:41
To polish or burnish a weapon until it gleams, sharpening an arrow or shaft. The Greek word never denotes this making-bright.Isa 49:2Jer 51:11
To sift, winnow, or refine by testing, separating the pure from the impure through trial. The Greek word does not carry this image of purity won by sorting and testing.Jer 4:11Dan 11:35Dan 12:10
It is used of a body being cleared of disease: a person with a skin disease asks to be made clean, is made clean, and can then be shown to a priest as fit again.Mat 8:3Mrk 1:42Luk 17:14
It reaches things and not only people, from dishes wiped on the outside while the inside stays foul to food that God himself pronounces fit to eat.Mat 23:25Luk 11:39Mrk 7:19Act 10:15
It is the working word of the worship system, where blood and sacrifice are what do the cleansing, and where the claim is pressed that such cleansing can reach the conscience and not just the outside of a worshipper.Heb 9:14Heb 9:22Heb 10:2
It reports the cleansing as something God or Christ has actually carried out for a people, so the person cleansed is the one receiving the act rather than the one attempting it.Tit 2:14Eph 5:261Jn 1:7
Both
Both are used for a person becoming clean before God as a matter of guilt and conduct rather than of dirt, and both can stand as a straight command to get clean.Isa 1:162Co 7:1Jas 4:8
Both can take the heart as the thing cleansed, though the Hebrew asks whether a person can clean his own heart while the Greek says God cleansed the heart through trust in him.Psa 73:13Pro 20:9Act 15:9
Both arrive in English Bibles through the same small set of words, chiefly "clean" and "cleanse", which makes the two look like one idea to a reader working from a translation.Psa 119:91Jn 1:9
Its central use is the courtroom question of whether any human being can come out clear of guilt before God, put as a question that expects the answer no.Job 15:14Job 25:4Pro 20:9
It can put God on the clean side of that question, saying that he is the one shown to be in the right when he passes sentence, so the party coming out clear is the judge and not the accused.Psa 51:4
It also names the verdict handed down about someone else, as when God refuses to count a trader innocent while his scales are rigged.Mic 6:11
Where it does describe an attempt at cleanness, the attempt belongs to the person himself and the text presses whether it can work at all, one speaker having kept his heart clean for nothing and another asking how a young man could keep his course clean.Psa 73:13Psa 119:9
Its home ground is removing the defilement that kept a person outside the camp and away from worship, so a healed man is pronounced clean and sent to the priest.Mat 8:3Mrk 1:42Luk 17:14
It covers plain household washing, the scrubbing of cups and dishes, which Jesus turns into a picture of a life polished on the outside and filthy within.Mat 23:25Mat 23:26Luk 11:39
It can report a verdict instead of a process: God pronounces foods clean and nothing about the food itself has changed.Act 10:15Act 11:9
It is the standard word for guilt being washed away, with blood and confession doing the cleaning rather than heat or filtering.Heb 9:141Jn 1:71Jn 1:9
Both
Both can describe God making people fit to come near him: the priestly line put through the fire so their offerings are acceptable, and a people cleansed to belong to God.Mal 3:3Tit 2:14
Both assume purity is what is left after something is taken away, whether that is the dross pulled out of silver or the guilt lifted off a conscience.Psa 12:6Heb 9:14
It belongs to the mine and the workshop: it is what fierce heat does to gold and silver, driving off everything mixed in until only the metal is left.Job 28:1Psa 12:6
It often functions as a grade of material, so a finished object is listed as being made of "refined" gold or silver, a claim about quality rather than about ritual status.1Ch 28:181Ch 29:4
It also covers straining a liquid, filtering the sediment out of well aged wine and drawing water up clear so it falls as rain.Isa 25:6Job 36:27
It is the word for curing a defiling skin disease, so that the healing and the cleansing are one and the same act: a man kneels and asks to be made clean and is, and ten sent off to the priests come clean on the way.Mat 8:2Mat 8:3Mrk 1:42Luk 17:14
It can name a verdict rather than a scrubbing: God pronounces something clean that people had treated as off limits, and the ruling itself is what makes it clean, with no change to the thing at all.Mrk 7:19Act 10:15Act 11:9
It covers plain household washing of objects, and that ordinary sense is what makes the rebuke bite: cups and dishes are scoured on the outside while the inside stays filthy.Mat 23:25Mat 23:26Luk 11:39
It is the standard term for what sacrificial blood achieves in worship, applied to the equipment of the sanctuary and to a worshipper's guilty conscience alike, so that the person may approach God at all.Heb 9:14Heb 9:22Heb 9:23Heb 10:2
Both
Both describe guilt being taken away from a person by God's own action rather than by anything the person manages: one promises that scarlet sins will come out snow white, the other says that God clears away all wrongdoing so the person stands clean.Psa 51:7Isa 1:181Jn 1:71Jn 1:9
Both are used of a whole group being made clean and set apart for God, worked on over time and readied for a day still to come, not just of one individual getting a fresh start.Dan 11:35Dan 12:10Tit 2:14Eph 5:26
In both, the cleanness reaches the inner person and is not a matter of appearances: hearts are made clean by trust in God, and the plea is for a washing that goes deeper than the surface of a life.Psa 51:7Act 15:92Co 7:1Jas 4:8
At bottom it is a color word, and it can be used with no question of guilt or worship anywhere in view: a stripped fig tree is described simply by the bare white of its exposed branches.Jol 1:7
Even when it does deal with sin, it works by color rather than by dirt: the result is a visible whiteness like snow, something a person could see, instead of a stain being washed off or a defilement removed.Psa 51:7Isa 1:18Dan 12:10
The same spelling carries a second, quite separate use with nothing to do with purity: shaping and firing mud bricks, which is the word behind the tower builders' plan and behind the forced labor quota in Egypt.Gen 11:3Exo 5:7Exo 5:14
What scholars say about katharizō
The lexica treat καθαρίζω as a single verb (from the adjective καθαρός, clean) with a coherent range: physical or medical cleansing, cultic or ceremonial purification, and ethical or spiritual purification (BDAG s.v.; Hauck, TDNT 3:413-431 on the καθαρός word group). The Septuagint uses it heavily to render Hebrew טהר across the purity legislation, which grounds the New Testament cultic and ethical uses in Israel's clean/unclean categories. Its application to leprosy is not a distinct lexical sense but the standard idiom for restoration from a defiling disease, since such a person was excluded until pronounced clean. The moral use in Hebrews and 1 John draws directly on the sacrificial cleansing language of the law, now referred to the blood of Christ.
Sources
BDAG, s.v. καθαρίζωlexicon
F. Hauck, "καθαρός, καθαρίζω, κτλ.," TDNT 3:413-431theological-dictionary
H. Balz and G. Schneider, EDNT, s.v. καθαρίζωtheological-dictionary