It may seem that the main goal of the parable of the lost sheep (Mt 18, 12-14; Lk 15, 4-7) is to make us aware how much God loves sinners and how deeply He wants to regain them. The Fathers of the Church, of course, knew that kind of interpretation, nevertheless very early in history they started to apply a completely different explanation to the lost and found sheep. Already in the 2nd century we can find the statement that the sheep is not a single sinner but the entire human nature, which got lost through the original sin committed by Adam and was found and renewed thanks to the incarnation of God’s Son. In the Antiquity, it was universally believed that human life had a common dimension. That belief was a great part of ancient philosophy as well as the biblical tradition. Some of the Fathers understood the communion even deeper than others as they imagined the humanity as a living organic entity. The concept of the ontological unity of human nature was developed mostly by three Fathers: Irenaeus (2nd century), Methodius of Olympus (died c. 311) and Gregory of Nyssa (died c. 394). All three of them used the parable of the lost sheep as an example that could explain this doctrine. Besides, two more Fathers, Origen and Ambrose of Milan, spoke about the unity of the humanity when they explained the parable of the lost sheep, though their interpretation of this unity is completely different. However all five Fathers have something in common, which allows me to compare their deliberations on the parable together.