John 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:

John 1:13 Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.

These verse’s explains clearly how saving faith is both the act of a single instant and an attitude of a life. To become a child of God, a person must “receive” from Christ. And following this act of faith, there must be a continual action of believing. Also in order for a person to be truly a child of God, that persons faith must continue in Christ for all things. When that person believes in the name of Jesus Christ and when they receive Him, they are born again, and are ready and willing to follow Him wherever He would lead them. But not all people are the sons of God.

(John 3:1-21) says

John 3:1 There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:

John 3:2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.

John 3:3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.

John 3:4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?

John 3:5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.

John 3:6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.

John 3:7 Marvel not that I said unto thee, Ye must be born again.

John 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.

John 3:9 Nicodemus answered and said unto him, How can these things be?

John 3:10 Jesus answered and said unto him, Art thou a master of Israel, and knowest not these things?

John 3:11 Verily, verily, I say unto thee, We speak that we do know, and testify that we have seen; and ye receive not our witness.

John 3:12 If I have told you earthly things, and ye believe not, how shall ye believe, if I tell you of heavenly things?

John 3:13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.

John 3:14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up:

John 3:15 That whosoever believeth in him should not perish, but have eternal life.

John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.

John 3:17 For God sent not his Son into the world to condemn the world; but that the world through him might be saved.

John 3:18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.

John 3:19 And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.