this "marriage certificate" is unique in all it's symbolism. Each and every
element to this painting is a story in itself. The dog represents fertility, the
shoes to the side - the bare feet, both represent the fact that this is a holy
union on holy ground (repeated in King Narmar's pallet , among several other
paintings and sculptures). The single candle aflame represents the divinity of
Christ. The mirror of the apostles again represents the holy unity. In the
mirror you will find Van Eyck in a self portrait painting this scene, as to
prophetess the fact that he was witness to the union, thus, reinforcing the
marriage certificate. Also, what is more so interesting of this painting is the
fact that the bride is shown to be pregnant, when, in fact, this is argued that
it is simply the fashion of the time. This woman is not pregnant, however, the
bedchamber curtain is open, showing that they are about to enter and will
consummate the marriage.
...

[re: Mar 03 20:52 Victoria Franciosa]

It is fun to note that for marriages in Europe the presence of a priest (and at
least 2 witnesses) is a "novelty", required only after the Council of Trent
(1563)! Before that the couple themselve, was responsible for performing the
wedding! at home!  Vows could be a simple as e.g. "Will you marry me?" "I will."
...
So this painting might depict the 'real' ceremony itself!?

I think witnesses were only 'used' when there was a social discrepancy between
the spouse (You need a witness when there might be trust problems! - e.g for an
accident or a duel!), indicating that the bride might have come from a poorer
background!?
 
Also note that the white wedding dress was made popular by Anne of Brittany in
1499. Before (and for quite some time after) that, a woman just wore her best
dress.