A Gospel believer believes that Jesus is the son of God and believes what he preaches;

but not yet repented and baptized, this person is not a Chrisitan.
Neither are lukewarm followers of the Gospel, for transgression against one of the commandments is a transgression against all of the commandments, says Jesus: Revelations 3: 15 and James 2: 10.

Jesus tells us: by faith we are saved. But those who believe, yet do not follow, lack that faith!
And so we see the truth in Jesus’ quote: “Many are called, but few are chosen”.