You MUST command the respect of your audience first.
It might take 90 seconds of silence on the stage and mic and audience (don't milk-it or all is LOST)
If you lose them (you audience half-way into your first song...sorry....you do not have what it takes to control a slightly inebreated crowd...you are not "worthy of respect."
Weddings are difficult, YOU are NOT the center of attraction....friendships from 5, 10, 15 years renewed are the focal point....(outside the ceremony.)
Look Dude/Dudette! You are BACKGROUND NOISE.... and if you are good enough.... hopefully....you were paid well for your distraction....and entertainment to those (wives/girlfriends/husbands) who had NO connection to the nuptuals. They were thankful you filled a void.