I’d like to tweak the answer to this question, too. I explain in the first comment on this post. 

95. Q. What is adoption?
       A. It is God’s goodness in receiving sinful rebels as his beloved children.

(Click through to read scriptural proof.)

• John 1:12

  But to all who did receive him, who believed in his name, he gave the right to become children of God … 

• Ephesians 1:5

  [H]e predestined us for adoption as sons through Jesus Christ, according to the purpose of his will… .

• Ephesians 5:1

  Therefore be imitators of God, as beloved children.

• Galatians 4:7, 31

  So you are no longer a slave, but a son, and if a son, then an heir through God.

  So, brothers, we are not children of the slave but of the free woman.

• 1 John 3:1-3

  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. Beloved, we are God’s children now, and what we will be has not yet appeared; but we know that when he appears we shall be like him, because we shall see him as he is. And everyone who thus hopes in him purifies himself as he is pure.