As I understand, it was not a play on words. Marcus corrected iCake.
iCake gave an example "Иисус воскресе" to illustrate the pronunciation of "Иисус". But we do not say like that. It is a fixed Easter greeting, a set phrase: "Христос воскресе" (or just "Христос воскрес" - in modern Russian, the ending "-е" is archaic here). Then iCake admitted it was his mistake.
A good question! Generally speaking, it depends.
And yes, I agree with everyone else on that.
Double consonants are never pronounced as two separate sounds in a row. There are 2 possibilities:
1) In most of cases, doubling a consonant letter makes no effect on its pronunciation. Double consonants often occur in loan words: теннис (sounds like [тЭнис]), пассажир "passenger" (sounds like [пасажЫр]), ассоциация (sounds like [асацыАцыя]), антенна (sounds like [антЭна]), баррикада (sounds like [барикАда]) etc.
Double Н is also frequent in native Russian suffixes of adjectives and adverbs. In many case it is also pronounced just as a single Н: сделанный "made, done" [здЕланый], искренне "sincerely" [Искрини] etc.
2) In some cases, a double consonant makes somewhat a single prolonged sounds (slightly longer than an ordinary consonant), but the difference is noticeable for native speakers. It is hard to formulate a common rule for that.
But please notice: it is always a prolonged sound when a word begins with a double consonant.
More examples (in addition to what iCake provided):
ведение (conducting, directing) but введение (introduction) - they sound differently;
вод (genitive plural of "вода" - water, i.e. something like "of waters") but ввод (bringing in) - they sound differently;
сор (rubbish, litter) but ссор (genitive plural of "ссора" - quarrel, i.e. something like "of quarrels") - they sound differently.
So, to practice initial double consonants: введение, вводить, ввод, ссора, ссориться, ссуда.
Typically, this happens due to a prefix added to the root: в+ведение, в+водить, в+вод ("в" adds the meaning of "in, into"); с+суда (loan, grant) ("с" adds the meaning of "off") etc. The words ссора (a squarrel) and ссориться (to squarrel) are interesting examples which do not have a prefix, it is rather the root itself which starts with the double С.
In some other cases double consonants also can sound distinctly (as a prolonged sound). Marcus provided some examples for them. In addition: мАсса, длИнный, стрАнный, кОнный, окОнный. тОнна etc. (I capitalized the stressed vowels). So, I agree it might depend on the stress position as well: when immediately after a stressed vowel, the lengthening is noticeable. But there are also some cases when it cannot be explained this way: поддавкИ, оттопЫрить etc. (prefix + root + suffix: под+дав+ки, от-топыр-ить).
General advice for a beginner: when in doubt, it's better to pronounce a double consonant prolonged. Sometimes it may sound as a hypercorrect pronunciation, but it is much better then ignoring consonant lengthening where it must be lengthened.