13 The grass withers, the flower of sinners dies away: what of the righteous? “The righteous shall flourish like a palm tree”. The ungodly are green as grass; “The righteous shall flourish like a palm tree.” By the palm tree he signifies height. Possibly he had also this meaning in the palm, that in its extremities it is beautiful: so that you may trace its beginning from the earth, its end in its topmost branches, wherein its whole beauty dwells. The rough root appears in the earth, the beautiful foliage toward the sky. Your beauty too, then, shall be in the end. Your root is fixed fast: but our root is upward. For our root is Christ, who has ascended into heaven. Humbled, he shall be exalted; “he shall spread abroad like a cedar in Libanus.” See what trees he spoke of: the righteous shall flourish like a palm-tree: and shall spread abroad like a cedar in Libanus. When the sun has gone forth, does the palm-tree wither? Does the cedar die? But when the sun has been glowing for some hours, the grass dries up. The judgment, therefore, shall come, that sinners may wither, and the faithful flourish.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)