This question has been answered by many Christian denominations, but let's see what God says through His word in answering it.
In order to find out what God says we need to go back to who the Bible says was the first of mankind. Genesis 1:26-27 tells us, "and God said, Let us make man in our image, after our likeness....so God created man in his own image, in the image of God created he him; male and female created he them." God called man "Adam". In Genesis 5:1 God begins the genealogy of Adam with himself. In Luke Chapter 3 the genealogy of Jesus goes back to declare that Adam is a son of God.
God set forth a pattern in all of creation that is called the "kind principle". Only the seed of a "kind" can produce another of the same. An orange tree can not produce an apple. A cat can not produce a dog. God cannot produce a son from an animal or beast. Children and Sons of God must have the seed of God in them. The seed of their Father.
In Leviticus 17:11 the Bible tells us that the life of the flesh is in the blood. It is the blood line of the DNA which determines a person's biological Father. It is the blood that gives the true identity of who that person is.
God says that Adam is his son and Jesus is his Son (Luke 3:22 and 38). Scripture tells us they are both sons of God.
Here is a story to illustrate what we are talking about:
There once were two male children born to a family. The first child was kidnapped at birth, and raised by a family that told him he was bad and evil. This is all the child knew about himself until one day he found out that these people were really not his real parents. When he becomes an adult he goes in search of his real father which brings him to a huge country estate. He goes through the front gate and as he travels the road to the house he is stopped by a man. After talking with the man they are both made aware that they are brothers. The second man is eager to take his brother to their father' house. As they make a turn in the road there lies before them a huge castle. The second son opens the door where their father is waiting, for the father had seen both men coming down the road and recognized that both boys belonged to him. However, when the first son comes to the door he does not consider himself worthy enough to take part in his father's home and insists in staying in the stables. He's willing to live on the estate, but only as a servant and not as a son.
Scripture tells us in Romans 3:23 that "all have sinned and come short of the glory of God." The word sinned is a verb, not a noun professing identity. The word glory is the identity of releasing our inheritance as a son of God. In Corinthians 15:22 we read, "For as in Adam all die, even so in Christ shall all be made alive." In Corinthians 15:27-28, "For he hath put all things under his feet...that God may be all in all".
What is the difference between a Christian and a Non-Christian? A Christian knows who their Heavenly Father is and through that relationship recognizes their identity as a son of God. Jesus opened the door to our Father's house and has shown us the way into that relationship.
A Non-Christian simply doesn't know they have a Heavenly Father that loves them. Do you know the life of the second son or are you still living the life of the first?
Jesus said, "It is Finished" in John 19:30. He completed the work of bringing the sons of God back to the Father over 2000 years ago.