Hey Joe, the issue is controversial because Giovanni Arnolfini, the man in the portrait, is recorded to have first married nearly 10 years after the painting. This painting was for a long time thought to have served as a proof of the wedding, but there are some symbolic inconsistencies atypical of a marriage portrait. For instance, in medieval times, marriage portraits often showed bride and groom holding right hands, whereas they hold left and right in this portrait. Witnesses and a priest were often present in older paintings as well, where there is none in this seemingly secular setting.