One of the questions which learners of Greek inevitably have is “how is learning this helpful?” In one sense, of course, most of what you can see in the Greek you can already see in a good translation (or a variety of good translations). Given that there are 1) lots of translations (at least in the major European languages) and 2) most learners of Greek don’t learn to a very high proficiency such that they are probably safer to just stick with reading translations, it follows that 3) the honest answer to this question in many instances is, “because learning this helps you build character,” or something like that.
However, for those with eyes to see and hearts to endure the arduous task of learning, there is much rewarding in seeing how the Greek texts unveils its meaning. There are lots of cool things going on in the text which are subtle and insightful. Not to mention it is always reassuring to see it in the original, not just in the translation you happen to be reading.
One such of these insights is the subtle use of verbal aspect to characterize the conversion of the demoniac in Mark 5.1-20.
On demons and verbs
The demoniac in this passage is associated with imperfective aspect at the beginning. First, consider the imperfect verbs which dominate in the description of this man in vv. 2-5:
2 καὶ ἐξελθόντος αὐτοῦ ἐκ τοῦ πλοίου εὐθὺς ὑπήντησεν αὐτῷ ἐκ τῶν μνημείων ἄνθρωπος ἐν πνεύματι ἀκαθάρτῳ, 3 ὃς τὴν κατοίκησιν εἶχεν ἐν τοῖς μνήμασιν, καὶ οὐδὲ ἁλύσει οὐκέτι οὐδεὶς ἐδύνατο αὐτὸν δῆσαι 4 διὰ τὸ αὐτὸν πολλάκις πέδαις καὶ ἁλύσεσιν δεδέσθαι καὶ διεσπάσθαι ὑπ’ αὐτοῦ τὰς ἁλύσεις καὶ τὰς πέδας συντετρῖφθαι, καὶ οὐδεὶς ἴσχυεν αὐτὸν δαμάσαι· 5 καὶ διὰ παντὸς νυκτὸς καὶ ἡμέρας ἐν τοῖς μνήμασιν καὶ ἐν τοῖς ὄρεσιν ἦν κράζων καὶ κατακόπτων ἑαυτὸν λίθοις
Imperfect verbs convey imperfective aspect. Imperfective aspect does not profile the temporal boundaries of the event, in other words, it tends to characterize events which are on-going for the entire period of time under consideration. The three primary sub-domains of imperfective aspect are: 1) progressive, 2) habitual, and 3) stative. One can picture them this way. Progressive represents events as underway; habitual presents events/states as so common for the subject at hand that, within a reasonable time period, they can be profiled as not having stage boundaries; finally, stative takes this to the extreme and presents states as though they are always underway, with no boundaries possible (within a reasonable time-span).
Mark uses the imperfective aspect to characterize this man as (habitually) out of control, wild, dangerous, unclean—his life is the embodiment of tohu-wa-bohu in human form.
After this, there is the exchange between Jesus and the demons speaking through the demoniac. At the beginning of their conversation it is fascinating how there is no obvious identity difference; it is unclear where the identity of the man ends and that of the demons begins. But this changes at v. 12 with a switch from a “he/him” talking (even when the multitudinous demons are selected as the speaker, as in vs. 9, καὶ λέγει αὐτῷ· λεγιὼν ὄνομά μοι, ὅτι πολλοί ἐσμεν “and he said to him, ‘My name is Legion, for we are many‘”) to a “they begged [Jesus].” After that point, the demons are never referred to again in the singular—even when it is customarily the case, as per Greek grammar, to use the singular with a plural neuter subject, as in v. 13:
καὶ ἐξελθόντα τὰ πνεύματα τὰ ἀκάθαρτα εἰσῆλθον εἰς τοὺς χοίρους.
And the unclean spirits, having gone out, (3rd plural they) entered into the pigs.
This change from singular referring to man + demons to a plural referring signals one thing clearly: Jesus is here to do business with the demons which have invaded this man and control him. It also sets the stage for a subtle, but I think important, change that takes place in this encounter with Jesus.
Back on our observations of verbal aspect, it pays to look closely at how the demonic is referred to in the rest of the pericope, and by whom.
The man formerly known as “demoniac”
The demonic is referred to by a nominal participle three times in vv. 14-20, as the narrative reaches its climax. While Jesus casting out the demons is central to this story, it certainly is not the climax, though it is really cool. It comes as no surprise to the reader of Mark up to this point that Jesus can cast out demons. The climax has to do with the extensive reporting of the way people responded to this miracle. Noting how the structure of the story pushes us to think carefully about the response various parties have to the miracle, there is value in close attention to these participles.
In v. 15 and v. 16 the man is referred to with an imperfective participle (aka, “present” participle). Remembering that imperfective aspect profiles an event as on-going, we see that the crowd is identifying the man as “the currently demonized one.” Here the stative sub-domain of imperfective aspect is in play.
It is intriguing that many English translations miss this distinction in the way the man is referred to. They turn the mention in v. 15 to “one who had been possessed by demons,” or some equivalent, and keep v. 16 as “demon possessed,” reflecting the imperfective participle there. In other words, they read it as though there is a perfective (aka, aorist) participle in the text in v. 15, rather than the imperfective one that is actually there. This impulse appears quite old. In Catena in Marcum, the commentator (exactly who this is at this point I’m not sure; wherever the text comes from it does not appear to be extant anywhere else) paraphrases this passage as follows:
καὶ εὗρον καθήμενον τὸν ἄνθρωπον ἀφ’ οὗ τὰ δαιμόνια ἐξεληλύθει, ἱματισμένον καὶ σωφρονοῦντα, καὶ παρὰ τοὺς πόδας τοῦ Ἰησοῦ καθήμενον
And they found the man sitting, from whom the demons had gone out, clothed and sane and sitting by the feet of Jesus.
This explanation makes logical sense within the development of the story—which I imagine is why so many English translations take it. After all, at this point the demons are no longer in the man, so characterizing him with an imperfective aspect participle is slightly odd. However, there does not appear to be any significant textual evidence supporting this reading—no variants are listed in Nestle Aland 28. Against this approach, I am inclined to think that the form of the participle Mark wrote is intentional…and important. I would suggest that the name “the demonized one” is given here from the point of view of the crowd. Even though they see he is sane, the name sticks. This becomes part of the framework for understanding what is wrong in their response to Jesus and what is right in the response of the man to Jesus.
Discipleship as the key
The cool thing, both from the point of view of verbal aspect and the pericope as a testament to Jesus, happens in v. 18. Here the narrator picks up his business again without reference to the point of view of the crowd. When the narrator has cause to refer to the “demoniac” he does so using a different verbal aspect participle: the perfective aspect. He calls him ὁ δαιμονισθείς. The perfective aspect profiles events as bounded, that is, it has in view the temporal boundaries of the events (the event is whole; the beginning and end are presented, as it were). Perfective aspect quite naturally, therefore, is used to convey events and states which held in the past but no longer do. This switch in aspect could be capture by an expansive translation such as “the man who formerly was demonized.” This little switch—difficult to bring out without expansive English renderings—is exegetical dynamite.
What we see here is the narrator indicating the decisive change contact with Jesus rendered on this man’s life. It is interesting that the change first appears here, when the man is seeking to follow Jesus, and not in the discussion of the crowd about what has happened to him. It would have been appropriate to appear there, since he was just as much “the man who formerly was demonized” then as in v. 18. However, it appears in conjunction with his step to become a follower of Jesus.
I don’t think that is a coincidence. There is a subtle theme (often not subtle at all) in Mark about becoming a follower of Jesus. It is not simply in encountering Jesus that the man is reborn to have a new name; rather, it is in his step to follow Jesus as a disciple that his rebirth occurs.
Sometimes, it pays to pay close attention to the little details. Verbal aspect included.
Burton cites this passage as an example of what he calls “the general purpose present participle,” which he describes as a present participle “used without reference to time or progress, simply defining its subject as belonging to a certain class, i.e. the class of those who do the action denoted by the verb,” Ernest De Witt Burton, Syntax of the Moods and Tenses in New Testament Greek (Grand Rapids: Kregel, 1976), 56. Burton has an Aktionsart-centered perspective on the verbal system, where the notion of “progress” is central to the “present” verbal system. This does not help him here. If we think of the core meaning of the imperfective (or the Present) as presenting progressing action, then participles such as this one fall afoul, since there is no obvious notion of progress in the verb and situation. Thinking in terms of aspect, however, we see that the imperfective aspect deals with profiling an event as unbounded. The characteristically on-going event of being “demonized” is the state of being “demonized,” which is part of the territory the imperfective aspect covers. In many ways the verbal aspect vs. “traditional” grammar debate is overblown in terms of exegetical results, but it certainly is insightful in describing how the Greek verbal system functions in a unified way.
 The following translations do this: NIV, NASB, CSB, CJB, CEV, (maybe Douey-Rheims), HCSB, TLB (reads this way, though highly manipulated, of course), NCB, NIrV, NLT, OJB
Some translation make both participles past-statives (“was or had been demonized”): KJV (though this could be read as stative in both instances; evidence of NKJV favors putting it here), NKJV, WEB, ASV
A few reflect the aspect of the participles in Greek: ESV, NET, LEB, RSV
 Catenae (Novum Testamentum), Catena in Marcum (recensio ii) (e codd. Oxon. Bodl. Laud. 33 + Paris. Coislin. 23 + Paris. gr. 178) (4102: 002) “Catenae Graecorum patrum in Novum Testamentum, vol. 1”, Ed. Cramer, J.A. Oxford: Oxford University Press, 1840, Repr. 1967.
 That there is some manuscript evidence at some point in time seems likely, given that a homily on this chunk of Mark from Isidore Glabas (1341/42-1396) has the following reading, virtually identical to the “paraphrase” in Catena in Marcum: Ἰδόντες δὲ οἱ βόσκοντες τὸ γεγενημένον ἔφυγον καὶ ἀπήγγειλαν εἰς τὴν πόλιν καὶ εἰς τοὺς ἀγρούς. Ἐξῆλθον δὲ ἰδεῖν τὸ γεγονὸς καὶ ἦλθον πρὸς τὸν Ἰησοῦν καὶ εὗρον καθήμενον τὸν ἄνθρωπον, ἀφ’ οὗ τὰ δαιμόνια ἐξεληλύθει, ἱματισμένον καὶ σωφρονοῦντα παρὰ τοὺς πόδας τοῦ Ἰησοῦ, καὶ ἐφοβήθησαν (Homily 28, section 9). Here the reading is presented as part of the text on which he is commenting, rather than as an expansive aside as in Catena. This differs in many ways from the text as it stands in the various critical Greek New Testaments. Obviously he is quite late, and I am not suggesting his evidence is of great value for establishing the original text here, merely noting that there probably was at least one text which read more or less like this.