Rembrandt's Return of the Prodigal Son
The Apostle Paul said to the Athenians, "'For in him (that is in God) we live and move and have our being.' As some of your own poets have said, 'We are his offspring.'" (Acts 17:28-29) So in one sense, all human beings are children of God because God is our creator. However, the New Testament teaches that, in a special sense of the term, God is the Father of those who believe in his Son Jesus Christ.
God is often referred to in the New Testament as the Father of Jesus. Peter wrote, "Praise be to the God and Father of our Lord Jesus Christ!" (1 Peter 1:3) And Paul makes clear that we are adopted as God's children through Jesus. "For he (the God and Father of our Lord Jesus Christ) chose us in him (that is in Christ) before the creation of the world to be holy and blameless in his sight. In love he predestined us to be adopted as his children through Jesus Christ."
How do we know if we are in Christ? How do we know if we have been adopted by the Father? In Ephesians 1:13 Paul says, "And you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit." We can know that we are in Christ, that we have been adopted by the Father, if we have put our faith in Jesus Christ.
There are many wonderful results of spiritual adoption just as there are with physical adoption. When we are adopted spiritually we can be sure of God's love for us.
A man was talking to a young person who was adopted by a family that already had one biological child of their own. This man wanted to find out how this adopted child felt about her parent's love. Therefore, he asked her, "How do you know that your mother and father love you?" Her response was, "Oh, they had my sister. But they chose me!"
Because the Father has chosen us in Christ and adopted us, we can be sure of his love for us.