Thats not all he says thats why you got things called chapters and verses. Lets read the WHOLE THING.
1 John 5
10The one who believes in the Son of God has the testimony in himself; the one who does not believe God has made Him a liar, because he has not believed in the testimony that God has given concerning His Son.
11And the testimony is this, that God has given us eternal life, and this life is in His Son.
12He who has the Son has the life; he who does not have the Son of God does not have the life.
Repeating: The one who does not believe God has made Him a liar, because he has not believed in the testimony that God has given concerning His Son
What is the testimony that is believed or not?
And the testimony is this, that God has given us eternal life, and this life is in His Son.
Ok so the "reprobate" the one who makes God a LIAR is the one who ---> DOES NOT BELIEVE GOD HAS GIVEN THEM ETERNAL LIFE, AND THIS LIFE IS IN HIS SON
So when the "reprobate" says "HEY, God doesn't want me to have eternal life, Jesus Christ did not die for me"
Is he really a LIAR? or is he HONEST?