Today it is commonplace that every family and institution makes some type of סעודה/party in honor of חנוכה. This article will explore the sources and reasoning behind this practice.
1
The first one to address this question is the מהרם of Rothenburg (quoted by the טור להלכה [1]) who says unequivocally that חנוכה parties are a סעודת הרשות, because חנוכה was not established for משתה ושמחה but rather for הלל והודאה.
The בח there asks גופא why this is so, unlike פורים. -?- The בח explains that the main decree by פורים was a punishment for benefitting from אחשורוש's party; to that end, it was decreed that the Jews be persecuted and have their bodies, which benefitted from food and drink of איסור, killed. Where they did תשובה, they then afflicted their bodies (אסתר ד:טו); which is why פורים was established for משתה ושמחה, namely to remember the עיקר הנס. By חנוכה, on the other hand, the main decree was a punishment for lack of enthusiasm and zeal for the עבודה in the בית המקדש, which is why part of the decree was to disrupt the עבודה. Where they did תשובה, they then did so by sacrificing their lives for the continuation of the עבודה; which is why חנוכה was established for הלל והודאה, which are an עבודה שבלב.
The טז [2] offers an entirely different reason for this disparity, namely that the נס פורים was מפורסם להצלת נפשות, for which there is שמחה in a physical sense, whereas by חנוכה - even though there was a ישועה from ה יתברך in battle, still - the military victory was not מפורסם על צד הנס; rather, only by the נרות was the נס מפורסם, which is why they were קובע להודות ולהלל, namely because from the נרות there was no particular שמחה in a physical sense (the הצלת נפשות that resulted from the military victory having been historically secondary in significance). To that end they made an עיקר from the נס המפורסם which demands gratitude more than celebration.
The לבוש [3] is מחלק between חנוכה and פורים in that by פורים there was הצלת נפשות whereas by חנוכה there wasn't; after all, the Greeks weren't looking to kill per se, but rather political/cultural submission which would have involved leaving our faith. The טז disagrees with this חילוק because one who causes someone to sin is worse than one who kills him [4]. The reason for this is because one who kills someone only makes that person lose their life in this world. One who causes someone else to sin, on the other hand, makes that person lose their life in the Next World as well. אליה רבה points out, however, [5] that the aforementioned principle is only true with regards to one who convinces someone to sin willfully, not one who forces someone to sin, because one who sins unwillingly does not lose their life in the Next World.
The בח himself, however, disagrees with the מהרם, based on the fact that גדולי הדור of the previous generations [6] made parties - the correctness of this practice being proven by means of an inference from the רמבם (חנוכה ג:ג) who says that חנוכה was established for שמחה והלל.
2
מגילת תענית says [7] that part of the reason for the establishment of חנוכה as a festival was the rededication of the מזבח.
דרכי משה suggests the rededication of the מזבח [8] as a possible reason why there is some מנהג of משתה ושמחה nevertheless. What is not entirely clear is which מזבח is referred to here. The מ"א [9] assumes this to mean the completion of the מלאכת המשכן. Now, even though the משכן was completed on כה כסלו, it still remained unused until ניסן, where it was formally inaugurated. To that end, כסלו (figuratively speaking) complained to הקב"ה of unfair treatment. 'ה reassured כסלו (again, figuratively speaking) that it would get its due by means of חנוכה. This is why the חנוכת המזבח of the משכן which took place in ניסן might be celebrated in כסלו.
אליה רבה and מלבושי יו"ט [5], on the other hand, disagree with the above resolution and say, by dint of this קשא, that the חנוכת המזבח referred to by the רמא is that of the חשמונאים.
ר אייזיק Tirnau adds [10] that they were נוהג to say מזמורים and many תשבחות at a חנוכה party so that it should be like a סעודת מצוה.
Conclusion
We have shown that numerous reasons for חנוכה parties are brought by the פוסקים, some even going so far as to say that they are obligatory. While there are those who complain about this practice as a recent innovation, we have seen that this phenomenon is actually quite an old one, as evidenced by the discussion among the פוסקים as to whether such parties are סעודות מצוה or סעודות רשות. -?-
ואחד המרבה ואחד הממעיט ובלבד שיכוון את לבו לשמים.
[1] או"ח תרע:ב
[2] שו"ע או"ח שם ס"ק ג
[3] או"ח שם סעיף ב
[4] רשי דברים כג:ט
[5] לבוש או"ח שם אות יד
[6] This is in consistent with the בח's assumption that anything done by the previous generations (especially the גדולי הדור thereof) must be correct if only because it was indeed done by them. Whether or not we, mere mortals, can understand why what they did was correct is hardly relevant, as our understanding of the הלכה plays little role in determining what the הלכה should be; rather, we must simply copy what was done by the previous generation, on the assumption that whatever they did must have been correct. See או"ח סי' סח וקיב for a good example of where else this שיטה appears in the בח. This would not seem to be the consistent approach of many other פוסקים, who instead prefer to determine הלכה objectively, by means of שקלא וטריא.
ואכמ"ל.
[7] פרק ט. In truth, מגילת תענית does not say explicitly that חנוכת המזבח was a factor in the establishment of חנוכה as a festival. In fact, מגילת תענית only references the miracle of the oil lasting for eight days. However, מגילת תענית then asks why, if the חנוכת המזבח in the מדבר lasted only seven days, does חנוכה still last eight days? If we take מגילת תענית at face value, then the entire question seem irrelevant: what does the חנוכת המזבח in the מדבר have to do with anything? The מפרשים infer from here that, evidently, the חנוכת המזבח in the מדבר was part of the reason for establishing חנוכה as a יו"ט in the first place.
This connection is brought out further by פסיקתא רבתי in פרשה ו אות א.
[8] טור שם ס"ק א
[9] שו"ע שם ס"ק ג
[10] ספר המנהגים [חנוכה הגהה כט]. Note that the רמא, where bringing this הלכה in שו"ע, does not say that such a party is like a סעודת מצוה, but rather that such a party is a סעודת מצוה.