God is the true testimony about His Son Jesus Christ and the purpose of His coming to earth to die for our sins. The second part of 1 John 5:10 says Anyone who does not believe God has made him out to be a liar, because he has not believed the testimony God has given about his Son. We either believe God or we don’t. Jesus is the Son of God and He died for all of us because He loves us. It’s a simple truth.