7 And not alone by what has been stated, but also by the parable of the two sons, the younger of whom consumed his substance by living luxuriously with harlots, did the Lord teach one and the same Father, who did not even allow a kid to his elder son; but for him who had been lost, [namely] his younger son, he ordered the fatted calf to be killed, and he gave him the best robe. Also by the parable of the workmen who were sent into the vineyard at different periods of the day, one and the same God is declared as having called some in the beginning, when the world was first created; but others afterwards, and others during the intermediate period, others after a long lapse of time, and others again in the end of time; so that there are many workmen in their generations, but only one householder who calls them together.
For there is but one vineyard, since there is also but one righteousness, and one dispensator, for there is one Spirit of God who arranges all things; and in like manner is there one hire, for they all received a penny each man, having [stamped upon it] the royal image and superscription, the knowledge of the Son of God, which is immortality. And therefore He began by giving the hire to those [who were engaged] last, because in the last times, when the Lord was revealed He presented Himself to all [as their reward].
Source: Adversus haereses (New Advent)