Child of God Spawn of Satan

Jesus can judge a man's salvation, but we have a much harder time making that determination. Jesus said He knew what was "in man" and you and I can never be 100% sure.

John 2:24 But Jesus did not commit himself unto them, because he knew all men, 25 And needed not that any should testify of man: for he knew what was in man.

John 5:42 But I know you, that ye have not the love of God in you.

John 6:64 But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him.

Jesus said every man needed to be "born again." Those only born of the flesh will die twice, dying both physically and spiritually. Jesus explained what He meant concerning being born again and this was contrasted a few chapters later in John chapter 8 with those who refused to be born of the Spirit.

Jesus rebuked the unbelievers and said that they were born of the Devil and called the Devil a liar, the father of lies and their father (John 8:41-44).

Although this passage certainly refers to every lost man as having the Devil as his father, it may also mean that there exists a spiritual birth substitute given by the Devil to those who hear and follow him. The Devil may give Christ-rejecting unbelievers a false religious experience in order to counterfeit the genuine experience offered by Jesus Christ (2Corinthians 11:3-4, 13-15).

At salvation, those who trust Christ receive the Spirit of God.
Ephesians 1:12 That we should be to the praise of his glory, who first trusted in Christ. 13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed...