Why does the world not know believers?
Scripture teaches that the world does not know believers because, as a result of God's love, believers are called the children of God. This new identity comes through believing the Gospel and receiving the indwelling Holy Spirit, which places them in Christ—a spiritual reality the world cannot recognize.
Les explains that First John 3:1 is written to believers, reminding them that the Father's great love has called them the sons, or children, of God. Because of what has happened to them—they believed the Gospel, God gave them the indwelling Holy Spirit, and placed them in Christ—the world does not know them. The world has not the Spirit of Christ and therefore is not His, so it cannot recognize the spiritual reality of believers' sonship. This fits beautifully with what Paul writes in Romans and Ephesians, showing that the world's failure to know believers is tied to the believer's Spirit-given identity in Christ.
Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not.