"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." (1 John 3:1)
When John says "behold," he uses the Greek word eido, which might well be here rendered "focus your mind," this fact is important! We are called "sons of God." The world can't know this because the world does not know God.
We are chosen (Ephesians 1:4), selected out of many who will not be so favored (Matthew 22:14), and adopted (Galatians 4:5) into the family of the omnipotent Creator, "to be conformed to the image of his Son" (Romans 8:29). Not only that, but since we have been created "after God in righteousness and true holiness" (Ephesians 4:24), then as God's "sons" we are "then heirs; heirs of God, and joint-heirs with Christ" (Romans 8:17).
This unique and priceless gift of sonship has the responsibilities of "sons" as well as the privileges. Yes, we are made righteous (2 Corinthians 5:21), but we are also called "unto holiness" (1 Thessalonians 4:7) and expected to "work out" our salvation (Philippians 2:12) with fear and trembling. Although we are granted rights to "sit together" with Christ in heavenly places (Ephesians 2:6), we are commanded to "put on the whole armor of God" here on earth so that we can "withstand in the evil day" (Ephesians 6:11, 13).
Sonship also demands the "chastisement" of the Father (Hebrews 12:8) and the careful additions to our faith of the character disciplines of virtue, knowledge, temperance, patience, godliness, brotherly kindness, and charity (2 Peter 1:5-7). Earthly sonship must "grow in grace, and in the knowledge of our Lord and Saviour Jesus Christ" (2 Peter 3:18). HMM III