What is the meaning of Jesus' first sign: the six jars, the water filled to the brim, the good wine saved 'til last?
Thanks for your question.
Here is a link to a book in PDF format available online. It is entitled The Eight Signs of John and was written by John Ullman of Perth Australia.
THE FIRST SIGN
Water Changed into Wine
THE PURPOSE TO ISRAEL, NATIONALLY:
To show that Israel were spiritually bereft, and that only the Son of God, their Messiah, could supply their spiritual needs and restore them to the Father.
THE MEANING TO SPIRITUAL ISRAEL:
To show that if we drink the "wine" of his doctrine, and become covered with the blood of his sacrifice, we can find joy in his service — a joy which will be fully realised at the glorious marriage supper of the Lamb.
God bless you,