I would say this is very close to zealot, or at least that would be a nice way of translating it, since zealotry was also originally connected with religion.

ЮРОДИВЫЙ и (обл.) ЮРОДИВЫЙ, юродивая, юродивое.

1. Глуповатый, чудаковатый, безумный. У каждого свой сказ про юродивого помещика. Некрасов.

2. в знач. сущ. юродивый, юродивого, м. Христианский аскет-безумец или принявший вид безумца и обладающий, по мнению верующих, даром прорицания (церк., религ.). Христа ради или во Христе юродивый. Молись за меня богу, юродивый! Пушкин.

ЮРОДСТВО, юродства, ср.

1. только ед. Намеренное старание казаться юродивым, глупым, безумным.

2. Бессмысленный, безумный, глупый поступок, какой мог бы совершить только юродивый человек. Бросьте ваши юродства! Говорите без юродства и не начинайте оскорблением домашних ваших. Достоевский.

1 Corinthians 4:10 (KJV)
We are fools for Christ's sake, but ye are wise in Christ; we are weak, but ye are strong; ye are honourable, but we are despised.

The Russian Orthodox Church believes these words of Apostle Paul are the basis of yurodivyy's' mission.

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Note added at 26 mins (2006-10-29 09:52:23 GMT)
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Other translations of the same verse from the Gospels

fools for Christ
fools because of Christ
Messiah's misfits
fools on account of Christ and for His sake
Our dedication to Christ makes us look like fools
Because of Christ we are thought of as fools
We are thought of as fools because of Christ

.

Blessed are the poor in spirit: for theirs is the kingdom of heaven. (Verse 3); Blessed are the meek: for they shall posses the land. ...
Catholic encyclopedia - English translation = "блаженны юродивые"

"Meek" is an equivalent I believe of the word as it stands in your context.

It knows also strange and unwonted paths to sanctification: that, for instance, of the 'fools in Christ', committing extravagant acts that their spiritual ...
www.orthodoxinfo.com/general/lossky_intro.aspx

The Holy fools, or fools in Christ, were itinerant ascetics who enjoyed great popularity among the ordinary people of Russia, many of them being revered as saints.
www.geocities.com/athens/delphi/6422/Page2.html

Before the nineteenth century Russian jurodivye (or fools in Christ) were described mostly in hagiographic materials and in travelogues of foreign visitors ...
aatseel.org/program/aatseel/2002/abstracts/Kobets.html

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Note added at 8 hrs (2006-10-29 17:54:19 GMT)
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the last link refers to an interesting article:

IURODSTVO
http://www.slavdom.com/index.php?id=35

Idiot is used in English versions of both the poem and the libretto

BORIS GODUNOV

A Drama in Verse

By ALEXANDER PUSHKIN

Rendered into English verse by Alfred Hayes
Boyars, The People, Inspectors, Officers, Attendants, Guests,
a Boy in attendance on Prince Shuisky, a Catholic Priest, a
Polish Noble, a Poet, *****an Idiot*****, a Beggar, Gentlemen, Peasants,
Guards, Russian, Polish, and German Soldiers, a Russian
Prisoner of War, Boys, an old Woman, Ladies, Serving-women

http://forum.stereophile.com/forum/showflat.php?Cat=0&Number...

Valery Gergiev, 1869 version

Part Four opens with a return of the Russian People Motif, and it has ***the requisite Idiot**** describing what has happened and what will be, if you will, while he implores the Tsar to kill the urchins who torment the Idiot, just like he killed the tsarevich. Ah, what Russian tragedy is complete without the ***Holy Fool***?

I believe here (discussing art) the Russian Юродивые is used more like "одержимость, одержимые" - people possessed \ obsessed with\by some ideas.