Dr. James Fleming writes,
"The watchtower is a tall structure built of field stone in the midst of steep, terraced vineyards. Often the vineyard is far from the village, and needs to be protected both from natural enemies and from thieves. The watchtower serves as temporary living quarters for the owners during summer. When the grapes become ripe in July, the family will be found camping out in the watchtower by night while harvesting the fruit during the day.
The watchtower is symbolic of divine protection:
"the name of the Lord is a strong tower; the righteous flee into it and are safe" (Proverbs 18:10)
"Let me sing to my friend the song of his love for his vineyard.He dug the soil, cleared it of stones, and planted choice vines in it. In the middle he built a tower, he dug a press there too." (Isa. 5:1-2, JB)
"Listen to another parable: There was a landowner who planted a vineyard. He put a wall around it, dug a winepress in it and built a watchtower." (Matt 21:33, NIV)
Special watchfulness was required before the grape harvest to guard the fruit from animals and thieves. But once the grapes were gathered, it was a time of joy. Singing and shouting accompanied the treading of the grapes (Isaiah 16:10).
To the ancient Israelites, the bursting grapes and shouts of joy suggested the destruction of enemies and the victory conquest. The fruit of the vine is often referred to as "blood" (Genesis 49:11) and the destruction of enemies as "treading" them underfoot. This image is extended to God, who is pictured in judgment as shouting "like those who tread the grapes" (Jeremiah 25:30), His garments stained with blood from the enemies trampled under His feet (Isaiah 63:2). "