This fruit was very precious, and the Lord of the vineyard really wanted it, because it had so many uses and so much value. It was a major cash crop for ancient Israelites, who exported olive oil. Not every place can grow olives because you have to have the right elevation and the right moisture. There are only certain places in all of the world where olives will grow: around the Mediterranean and North Africa, in central Chile, and southern and central California, in particular.
The first pressing of the olives produces the purest and most valuable oil because it is more highly concentrated. It actually comes out looking a little red the first time. This oil was used for anointing and for offerings as the first-fruits or the first oils.
Truman G. Madsen, "The Olive Press: A Symbol of Christ," in The Allegory of the Olive Tree: The Olive, the Bible, and Jacob 5, ed. Stephen D. Ricks and John W. Welch (Provo and Salt Lake City, UT: FARMS and Deseret Book, 1994), 1–10.
John Gee and Daniel C. Peterson, "Graft and Corruption: On Olives and Olive Culture in the Pre-Modern Mediterranean," in The Allegory of the Olive Tree: The Olive, the Bible, and Jacob 5, ed. Stephen D. Ricks and John W. Welch (Provo and Salt Lake City, UT: FARMS and Deseret Book, 1994), 186–247.