17 “You have made all the ends of the earth”....Behold in what manner He has made the ends of the earth, that has wrought Salvation in the midst of the earth. “You have made all the ends of the earth. Summer and spring You have made them.” Men fervent in the Spirit are the summer. You, I say, hast made men fervent in the Spirit: You have made also the novices in the Faith, they are the “spring.” “Summer and Spring You have made them.” They shall not glory as if they have not received: “You have made them.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)