During Christ Jesus' farewell discourse with his apostles, See John, chaps. 14-17 . it is implied more than once that his followers would have a special challenge and blessing in their work because they were "not of the world."
The Master also prayed to keep these beloved followers in unity. Jesus must have realized the apostles would encounter new trials when he would no longer be with them. They would be left with the full responsibility to ensure that the saving message of Christianity reached mankind. And the work to be done could never be accomplished in the seclusion of an ivory tower, in isolation from humanity. Jesus continued his prayer to God: "I pray not that thou shouldest take them out of the world, but that thou shouldest keep them from the evil. They are not of the world, even as I am not of the world." John 17:15, 16.
Christian discipleship is not of the world—not devoted to the mere pursuit of material pleasures; not submerged in the desires and wants of the carnal mind; not serving mammon; not worldly-minded. But the gift of Christ's redemption surely needs to be shared with all mankind, in the world. It is, after all, the world's material-mindedness—with its sin, disease, limitation, and death—that is to be transformed by divine Truth. The grace of God, manifest in the saving action of His Christ, regenerates the individual. It changes one's heart, awakens one's innate Christliness, and reveals holiness, harmony, freedom, and life eternal—the special fruits of spiritual-mindedness.