They shall still bring forth fruit in old age
Being thus planted and watered, they shall not only bring forth the fruits of righteousness, but shall continue, and go on to do so, and even when they are grown old; contrary to all other trees, which, when old, cease bearing fruit; but so do not the righteous; grace is often in the greatest vigour when nature is decayed; witness Abraham, Job, David, Zachariah, and Elisabeth, and good old Simeon, who went to the grave like shocks of corn, fully ripe:
they shall be fat and flourishing;
or "green", full of sap and moisture, abound with green leaves and precious fruit; or, in other words, abound in grace, and be fruitful in every good work: being ingrafted into the true olive, the church of God, they partake of the root and fatness of it; having a place in the house of the Lord, they are satisfied with the goodness and fatness thereof, and are made to drink of the river of divine pleasure; and being in the courts of the Lord, where a feast of fat things is provided for them, they eat and feed, and so thrive and flourish; the allusion is to fat and flourishing palm trees F7.
F7 "Praeferat Herodis palmetis pinguibus----". Horat. Ep. l. 2. Ep. 2. v. 148.