@Martin S.: As hein has pointed out, 'before' can also have a spatial meaning in English. It may sound a shade archaic, but it survives in formal phrases such as 'appear before a court of law.'
AFAIK this particular expression is biblical in both languages, from the description of Nimrod:
a mighty warrior before the Lord (Genesis 10:9)
ein gewaltiger Jäger vor dem Herrn (1. Mose 10,9)
I tend to agree with everyone who has said that the translation probably shouldn't be literal, as the phrase isn't widely used in this kind of context in English (though if you dig you might find a few examples). Either Sonnenkult's or nina's suggestion should be fine. If you wanted to try for the allusion, though, 'a mighty wanker before the Lord' might fly (though just barely) among traditionally educated readers.
BTW, 'wanker' is BE; in AE you would need 'jerk,' which is milder, or 'jerk-off,' which is less common, or just some other more general term of abuse. In this case, though, the 'w_____r' similarity seems too lucky a coincidence to pass up.