Symbolism: The action of the story now begins. When the Lord sees Israel’s apostasy, his response is not anger, nor an impulse to destroy, but rather concern and a hope to salvage. The pruning, digging, and nourishing are attempts to cut back the decayed wood so that the tree’s remaining life force is concentrated in the still vital growth.
What in God’s relationship to humankind parallels this nourishing, digging, and pruning? I interpret it as the Lord’s efforts in sending prophets with messages of comfort or calls to repentance, either to nourish or to prune us, as we require.
Repentance prunes off the “decayed” part of Israel; because it turns to Yahweh, the tree is returned to a more vital whole. God’s word to the prophets also nourishes the obedient. By sending prophets to Israel, Yahweh accomplished acts parallel to those of a gardener in pruning and fertilizing.
This step is the logical first step in revitalizing a tree. It can have an effect but is less invasive than the efforts that will follow. The spiritual parallel is the care with which God nurtures all of his children—that he will call us gently to repentance before sending more drastic witnesses and judgments.
Literature: There is a mild emphasis in verses 4 and 5 on promise/fulfillment. In verse 4 we have Yahweh’s “word,” the declaration of intent. In verse 5 we have the accomplishment of that intent. The explicit paralleling of intent/fulfillment highlights Yahweh’s trustworthiness. What Yahweh says through his prophets will come to pass, just as this master of the vineyard promises, then fulfils that promise.