A Commitment Ceremony is the traditional gargoyle celebration marking a couple's union. Considering gargoyles mate for life, the ceremony is significant to Gargoyle culture. ("Masque")
A Commitment Ceremony is presided by another gargoyle (one mostly likely interested in matters of spirituality, like Coldfire) and Seconds are chosen by the couple to be in attendance. There does not appear to be a limit to the number of Seconds the couple may ask. ("Render Unto Caesar") 
By 1999, Goliath and Elisa will have their own sort of Commitment Ceremony.  Friends and relatives will be in attendance. 
As early as 1997, very little has been revealed about what a Commitment Ceremony would entail for Goliath and Elisa.  It was later clarified to be unique to gargoyle custom.