What Tertullian or Irenaeus wrote is immaterial as the question was regarding what the Scriptures say. However, the first reference given to support Postmillennialism was Joel 2:28-32. The very next verse is Joel 3:1, 2 - "For then, in those days and at that time, when I restore the fortunes of Judah and Jerusalem, I will gather all the nations and bring them down to the valley of Jehoshaphat, and I will enter into judgment with them there, on account of my people and my heritage Israel, because they have scattered them among the nations. They have divided my land," Do you believe this will happen or does "Judah," "Jerusalem," "my people and my heritage Israel," and "my land" have another reference? I would be more than willing to examine each of these references as you expressed an interest to do so.