it's one of the 5 things you need to abstain from in order to go to a holy event
even weddings you can't drink before the afternoon/evening when all the religious stuff has happened (guy came to my wedding, a mate of a mate, and he sparked up a smoke in the temple, he got beaten up and thrown out and bought shame upon his friend who'd bought him along)

you'll also notice that the vast majority of peole in the pictures have their head covered as a sign of respect because they are in gods house, even though they aren't on temple grounds, god is everywhere so we show respect that way

different parts of sikhism perceve things in subtle but different ways, but the central belief is that if you are good and treat others well, you can live a happy life