1 John 4:20

4:20 If anyone says “I love God” and yet hates his fellow Christian, he is a liar, because the one who does not love his fellow Christian whom he has seen cannot love God whom he has not seen.

1 John 5:10

5:10 (The 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 testified concerning his Son.)