Within Christianity, there are different groups, or denominations, due to different beliefs.

The one thing that binds all truly Christian churches together however is their belief that salvation (eternal life) is found in no one else other than Christ Jesus; that there is no other name under heaven given to men by which we must be saved.¹  Also, their belief that Christ Jesus is God in the flesh, God-man (fully God, fully man.)² 

Bible References:

¹ (Acts 4:12)

² (Colossians 2:9)