1 John 3:1
 See what kind of love the Father has given to us, that we should be called children of God; and so we are. The reason why the world does not know us is that it did not know him. (ESV)
The Apostle John goes into a celebratory statement here. He revels in the fact that we are called children of God. This is a direct result of the amazing love that the Father has given to us. It is a most astonishing thing that we can be called children of God. Have you ever thought about that? Are you overwhelmed with joy that you can be called God's child? What makes it so amazing is that we are not the most lovable, and certainly not deserving of God's love at all.
Consider what the Apostle Paul said concerning the state of natural man before God the Father chose to love us:
 And you were dead in the trespasses and sins  in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience— among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind. (ESV)
We were dead in our sins. We were children of God's wrath. We were followers of the prince of the power of the air (that is, Satan). That changes the picture a bit, doesn't it? The fact that we are now children of God is an amazing thing. Those who are now God's children were formerly objects of His great wrath, followers of Satan himself. This is why John can be so thrilled to declare that because of the love of God we are now called children.
The great Charles Spurgeon was also overwhelmed at how great a Savior we have in Christ that enables us to be called God's children:
"My hope lives not because I am not a sinner, but because I am a sinner for whom Christ died; my trust is not that I am holy, but that being unholy, HE is my righteousness. My faith rests not upon what I am or shall be or feel or know, but in what Christ is, in what He has done, and in what He is now doing for me. Hallelujah!"
- Charles Spurgeon
Are you God's child? If not, why not place your faith in the great work of Christ on your behalf? Because of His amazing love you can become a child of God. Hallelujah!