The command is given to make a candelabrum of seven branches in the Tabernacle. A detailed description has already been given to Betzalel much earlier in Exodus and now that the Priesthood has been established and Aharon and his sons have been “dedicated”, they are commanded to make sure that lights should burn on this “menorah” perpetually.
The Seven Branched Candelabrum became the national symbol and was far more widely recognized, and for longer, than the Star of David. Historians and archaeologists still argue as to the origin of the Star of David, but the candelabrum is certainly our earliest recognizable national symbol (as opposed to the symbols of the individual tribes).
Yet even here there is plenty of disagreement. Most of us were used to the representation of the menorah from reproductions of the sculpture on Hadrian’s Arch, which depicts the victorious Romans carrying off booty from the sacked Temple in Jerusalem two thousand years ago. The branches are curved and the base is solid, as opposed to the Biblical instruction for there to be “legs”. And in recent years Lubavitch has made a feature of using the straight angular-branched version that Maimonides mentions “though the vast majority of the other commentators and experts disagreed.
Then there is the issue of how many lights and for how long they were lit. The Torah is ambiguous, on the face of it. The full seven lights were lit to coincide with certain public ceremonies. The wicks were arranged so that they all pointed towards the center. But the western most light alone kept burning all the time and this is the origin of the Ner Tamid, the Eternal Flame, that burns in front of the ark in synagogues today.
Chanukah is the commemoration of the period under Greek rule when the Temple was desecrated and only Judah Macabee’s interventions allowed the Temple to be rededicated and the menorah to be relit.
But of course on Chanukah we have an eight branched candelabrum. There has always been a ban on trying to replicate Temple artifacts. As a result some people do not call this eight-branched Chanukah candelabrum a “menorah”, but a “Chanukiah”.
The eight-branched is the most popular; most Jewish homes have one. But the seven-branched one is the one and only authentic original.