That no one should be uplifted in his labour
In Solomon, in Ecclesiasticus: “Extol not yourself in doing your work.” Also in the Gospel according to Luke: “Which of you, having a servant ploughing, or a shepherd, says to him when he comes from the field, Pass forward and recline? But he says to him, Make ready somewhat that I may sup, and gird yourself, and minister to me, until I eat and drink; and afterwards you shall eat and drink? Does he thank that servant because he has done what was commanded him? So also you, when you shall have done that which is commanded you, say, We are unprofitable servants; we have done what we had to do.”
Source: The Treatises of Cyprian (New Advent)