Each element in a parable, being a short story, is indispensable to the plot, but may or may not have metaphoric significance. Let us treat these two aspects separately.
Plot Element: Stones
In the parable of Isa 5, the clearing of stones had a dual function:
- To remove impediments to growing plants in unhindered soil
- To use the stones to create a wall around the vineyard which both delineated the extent of the master's ownership and offer protection from intruders (whether human or animal)
For an example of the opposite process to make a piece of land useless for agriculture, see 2 Kings 3:19 where stones are thrown on a field to ruin it.
Metaphoric Significance of Stones
It is not essential that each and every noun in a parable have significance. Do the stones have significance or the clearing of stones have significance?
Commentators are divided about this. Elsewhere, stone represents the kingdom of Jesus (Dan 2:34, 41-45); but stone can also represent false gods and idolatry (Rev 9:20, Deut 28:36, 64, 2 Kings 19:18, Eze 20:32, Dan 5:4, etc). For example ellicot says this:
in the “stones” that were gathered out, the removal of the old
idolatries that would have hindered the development of the nation’s
life; in the “tower” of the vineyard (comp. in a different context
Isaiah 1:8), the monarchy and throne of David, or the watch-tower from
which the prophets looked forth (Hab. Ii. 1; Isaiah 21:5-8);
Benson has a different view:
gathered out the stones thereof — Which otherwise might have marred the land, (2 Kings 3:19,) and injured the vines. In other
words, he removed all the hinderances of fruitfulness. In that he
formed his church of the posterity of those wise, holy, and faithful
men, Abraham, Isaac, and Jacob, and purged and reformed the nation in
the wilderness before he established them in Canaan, he might truly be
said to plant his vineyard with the choicest vine
We could continue speculating but the safest is to allow the parable in Isa 5 to explain itself:
- V4: What more could I have done for My vineyard than I already did for it?
- V7: the vineyard represents the house of Israel
- V7: the men of Israel are represented by the vines
- V4, 8-20: the sour grapes represent Israel's sinful behavior
- V5: the wall represented God's protection which he will tear down and allow people to trample the vineyard
Thus, according to the parable itself, only a few elements of the story have direct spiritual significance: the wine press is not mentioned, the watchtower is not mentioned, etc.
However, according to the above explanation, the wall around the vineyard representing God's protection, made from the stone found in the original field, represents God's divine protection which will exist only so long as Israel remained loyal to God. In the absence of such loyalty, the wall is removed and the field is trampled (compared Luke 21:24).