The specific usage of the "(" and ")" symbols in various translations was indeed added, as those symbols did not exist in Greek at the time. But the text
within them in Mark 7:19 was in the Greek and was
not added by the translators as you have claimed. It's right there at the end in the Greek: "καθαριζων παντα τα βρωματα." That's not added; that's in the text. This is translated out in the NIV as "(In saying this, Jesus declared all foods clean.)" or the NASB as "(
Thereby He declared all foods clean.)" and the ESV as "(Thus he declared all foods clean.)"
I'm not really fond of the usage of parentheses here. They're used to try to indicate that this was a remark by the author of Mark, but unfortunately it clearly confuses people who think it is a sign that the text was not in the original Greek.
Given there is some misinformation about this portion of the verse, it might be good to go about explaining it, as the way one arrives at this translation, due to involving some constructions in Greek that do not actually exist in English, requiring the translator to get into some bits of awkwardness.
(Disclaimer: I am not an expert on Greek. But everything I am about to say is, as far as I can tell, very accurate, and strongly based on information I have found from people who
are experts on Greek)
The last three words are simple enough, meaning "all (παντα) the (τα) food (βρωματα)". Therefore, what concerns us is the first word, καθαρίζων. This verb means to clean or purify, including the meaning of to pronounce something clean (see Acts 10:15 and Acts 11:19). In this specific case, the verb is in the Nominative Masculine Singular version of the Present Active Participle form. That may have sounded like gibberish, but to try to make it simple, the Participle form of a verb has several uses, which are explained well
here. From context, it is obvious it is not the adjective or substantive use (#1 or #2) so it is adverbially (#3). In other words, this verb is connected to another verb. There are several ways the adverbial use can be used, but all boil down to it being used in connection with another verb, such as to say that one verb caused the other, or they are being done at the same time.
Now, καθαρίζων, as noted, is Present and Active. That means it's in the present tense and is active (as opposed to passive; it is the difference between "I eat food" (active) versus "the food is eaten by me" (passive)). That is, the subject is
doing the action rather than having it done to them.
More important, however, is that καθαρίζων is the Nominative Masculine Singular. Nominative Masculine Singular means that means the subject is in the nominative case (Greek nouns, as well as things that modify them like adjectives, have different cases depending on grammar--nominative normally denotes the subject of a sentence), is masculine, and is singular. In other words, some masculine singular noun is doing something, and the καθαρίζων is accompanying that other verb. Most verb forms in Greek do not specify the gender of its subject, but this one does.
Thus, to figure out how this all fits together, we have to look for another verb that is being done by a masculine noun. There is, as far as I can tell, only one that fits: The earlier part in Matthew 7:18 where the subject is Jesus and the verb is "said" (the word Jesus is not stated, but is to be inferred). There is no other masculine nominative noun that has an accompanying verb that I see ("sewer" is masculine, but there is no accompanying verb for it, and furthermore is accusative rather than nominative). So it is saying that, in conjunction with Jesus
saying something, Jesus cleansed all food or declared all food clean. However, due to the verbs being separated by a bunch of dialogue, and English not having a participle form that can function as this, the translations have to try to express this connection by adding things. The ESV's "Thus he declared all foods clean" therefore adds the word "thus" (the NASB uses thereby) to convey this. The NIV, which is not as literal of a translation, tries to make it more clear by restating the original verb and noun that is being linked more clearly, with "In saying this, Jesus declared all food clean."
So, no, the parenthetical was not the addition of any translator, but was in the text. Again: καθαριζων παντα τα βρωματα is in the Greek.
But wait, someone might ask. Don't older Bibles render it differently, such as most notably the KJV? Compare the KJV with ESV in Mark 7:18-19:
KJV:
And he saith unto them, Are ye so without understanding also? Do ye not perceive, that whatsoever thing from without entereth into the man, it cannot defile him; Because it entereth not into his heart, but into the belly, and goeth out into the draught,
purging all meats?
ESV:
And he said to them, “Then are you also without understanding? Do you not see that whatever goes into a person from outside cannot defile him, since it enters not his heart but his stomach, and is expelled?”
(Thus he declared all foods clean.)
Part of the difference is linguistic drift ("meats" and "purge" had somewhat different connotations back then), but we see a difference beyond that. So, why does the KJV (and other Bibles from around that period, like the Geneva Bible) just have "purging all meats" instead of something like "Thus he declared all foods clean"? It's not an issue of translation so much as a difference in the Greek text itself. The bolded section in the ESV and other modern translations was translated from "καθαριζ
ων παντα τα βρωματα" but the KJV was translated from "καθαριζ
ον παντα τα βρωματα". The difference is a single letter, ω vs, ο, but this actually changes the meaning and translation.
You see, if you have the ο in καθαριζον, then it's in the
Neuter Nominative Singular form. Jesus works fine with a
masculine form of the verb--as, grammatically speaking, Jesus is a masculine noun--but with this, we need to look instead for a
neuter subject instead. But the only neuter nominative singular I see is the word παν (meaning everything, translated as "whatsoever thing" in the KJV and "whatever" in the ESV) and which is mentioned in Mark 7:18. This is actually an adjective of an unspecified noun--you can do that in Greek, use adjectives without the noun if the reader can figure it out from context--but we know the noun in question is neuter and singular by παν, as it is used with neuter and singular nouns (in terms of cases, it can be used for nominative, accusative, or vocative). Therefore, the unspecified "everything" noun works fine with the neuter nominative singular καθαριζον. And the "everything" is doing something also, namely going through the stomach and exiting. This gives us the statement that everything that goes through the digestive system and into the sewer purges all food (not that the digestive system or sewer is doing the purging, bur rather the stuff going through it purges the food). This seems a bit odd--the food is being purged by
other food?--but if you're working with the neuter form it seems it's the best you can get. The KJV translates accordingly.
So, why the difference in the Greek text? The reason for this difference is due to them having different text bases. The KJV is translated from the Textus Receptus, a Greek text put together by a Catholic priest named Erasmus which he made after looking at several Greek manuscripts and choosing what he thought were the best readings from them. The Textus Receptus is not without its issues, one of the most obvious ones because he really only had a few manuscripts to work with, resulting in some rather questionable readings (one particularly notorious case is how his manuscript of Revelation lacked the ending, so for that final portion he back-translated from a Latin version of Revelation to create the Greek). Later textual bases, like the Nestle-Alend text that a lot of new translations are primarily or entirely based on, involve looking at more manuscripts than just a handful in order to get more accurate readings. And this results in the usage of καθαριζων (masculine) instead of καθαριζον (neuter).
I'm hardly an expert on textual criticism so I can't exactly mount a big argument on why to use the masculine form rather than the neuter beyond what amounts to an appeal to authority (that is, the experts say this is believed to be the original reading). But, I will note that of the earliest manuscripts of Mark 7:19 that we have, four of the five have καθαρίζων (masculine) and none have καθαριζον (neuter); if you are wondering, the fifth one has καθαριζει (a quite rare reading), the simple third person present active singular, which I believe could be understood in both manners. Those that quoted it--Origen, Gregory of Nyssa, John Chrysostom--all have καθαρίζων (masculine), or at least that's what
GNT Reader tells me. So there's definitely a strong case that the version used in the modern translations is the original one. The theory as to how the neuter form of καθαριζον got introduced into some manuscripts is that a scribe, confused about the apparent lack of a masculine noun nearby, thought that καθαρίζων (masculine) was an error and switched it to καθαριζον to correct it.
tl;dr: The words in parentheses (e.g. "Thus he declared all foods clean") were NOT added by the translators. They're right there in the Greek text: "καθαριζων παντα τα βρωματα".