Ambrose of Milan

When Jerubbaal, as we read, was beating out wheat under an oak, he received a message from God in order that he might bring the people of God from the power of strangers into liberty. Nor is it a matter of wonder if he was chosen for grace, seeing that even then, being appointed under the shadow of the holy cross and of the adorable Wisdom in the predestined mystery of the future incarnation, he was bringing forth the visible grains of the fruitful corn from their hiding places and was [mystically] separating the elect of the saints …

On the Holy Spirit, Book 1.1 ↗