Exegesis:
genomenēs hēmeras eukairou ‘an opportune day arriving’: for the use of the participial genitive clause to express time, cf. 6.2, genomenou sabbatou ‘when the Sabbath came.’
eukairos (only here in Mark) ‘timely,’ ‘opportune,’ ‘suitable’: so most translations; some, however, hold that the meaning here is ‘a festal (day)’ (cf. Moulton & Milligan) – Moffatt and Goodspeed give it this meaning.
tois genesiois autou (only here in Mark) ‘on his birthday’: properly the dative of the neuter plural of the adjective genesios ‘relating to (one’s) birth,’ with the meaning ‘birthday celebration’ (for the use of the plural cf. ta sabbata ‘Sabbath’ in 1.21).
deipnon epoiēsen ‘he gave a banquet.’
deipnon (12.39) ‘a formal meal,’ ‘a banquet,’ ‘a dinner.’
poieō ‘do,’ ‘make’: for its use in the sense of giving a banquet.
tois megistasin (only here in Mark) ‘chief men,’ ‘nobles.’
tois chiliarchois (only here in Mark) ‘high-ranking military officers’: the chiliarchos, leader of 1000 soldiers, was equivalent to the Roman tribunus militum, commander of a cohort (about 600 men). The word is used here in the general sense of high-ranking officers.
kai tois prōtois ‘and the most prominent men (of Galilee)’: cf. Lagrange, ‘the aristocracy of the country.’
prōtos (9.35; 10.31, 44; 12.20, 28, 29; 14.12; 16.9) ‘first.’
Translation:
Opportunity is ‘the right time’ or ‘a special time,’ but to make sense one must sometimes specify for whom such an occasion was opportune. Obviously, the proper person would be Herodias, viz, ‘a day for Herodias’ (Southern Subanen).
Birthday must usually not be translated literally, as has been done in some languages. For this was not the day of Herod’s birth, but the day on which he celebrated his birth. (As the result of one translation the people were very much amazed at the precocious nature of the baby Herod, for according to the Scriptures he apparently put on a banquet on the very day of his birth and was much impressed by the dancing of Herodias’ daughter.) Equivalents of birthday are quite varied: ‘day he was remembering his birth’ (Yaka), ‘when day of his birth comes up again’ (Chicahuaxtla Triqui), ‘day when he completed another year’ (Eastern Highland Otomi), and ‘day of his year’ (Chol).
Gave a banquet may be rendered as ‘provided much food’ or ‘caused to get together to eat’ (Copainalá Zoque). The giving of a feast is such a widespread custom in so many societies that there are usually no special problems in finding a satisfactory equivalent,
Courtiers and officers and the leading men of Galilee represent three classes of people: (1) the civil government, officials, (2) the military officers, and (3) the leading citizens of the realm, i.e. members of influential, rich families. This phrase can be rendered as ‘his under-rulers (i.e. those beneath him), and the rulers of his soldiers, and the wealthy people in Galilee.’ (Wealth and social prestige were as much equated in Biblical times as they are today.) In some languages leading men are ‘the chiefs’ or ‘the headmen’ (Navajo).
Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on the Gospel of Mark. (UBS Handbook Series). New York: UBS, 1961. For this and other handbooks for translators see here .