Christianity is a personal relationship with Jesus. Without this personal relationship, Christianity is just a religion in the same sense as any other.
Only in Christianity can you - indeed must you - have a personal relationship with God the Father through His Son Jesus.
All other religions teach that they will show you the way to god, only Jesus says I am the Way, The Truth and The Life.
Atheists and Agnostics may not consider their beliefs a religion, but they are indeed a faith.