First let me say I am a non drinker all my life and I do not advocate drinking to you here.
These verses clearly imply that they were already drunk when Jesus gave them more. Anyone who is drunk will not be able to stay awake for long when the alcohol is gone. Also the master of the banquet would have known right away that it was wine or not.
John 2:7 NIV
7Jesus said to the servants, “Fill the jars with water”; so they filled them to the brim.
8Then he told them, “Now draw some out and take it to the master of the banquet.”
They did so,
9and the master of the banquet tasted the water that had been turned into wine. He did not realize where it had come from, though the servants who had drawn the water knew. Then he called the bridegroom aside
10and said, “Everyone brings out the choice wine first and then the cheaper wine after the guests have had too much to drink; but you have saved the best till now.”
11This, the first of his miraculous signs, Jesus performed at Cana in Galilee. He thus revealed his glory, and his disciples put their faith in him.
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King James Bible
And saith unto him, Every man at the beginning doth set forth good wine; and when men have well drunk, then that which is worse: [but] thou hast kept the good wine until now.
God knew that the master of the banquet would be disgraced if the Wine ran out, because everyone would leave and go home.
The other reason of the importance of alcohol is that it was necessary to keep any drinking liquids from going rancid and becoming spoiled with algae and other microbes.They did not have refrigeration to keep grape juice fresh. Water for long voyages on ships had to be mixed with alcohol in casks to keep it safe to drink. Also this is probably where wine was invented in the first place as fermenting was a form of spoilage.
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