Whether we are believers or not, if we sin the only way given for salvation is according to Christs commandment given to his Disciples.
It is all through Jesus.
Rom 3:25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God;
1 Jn 2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
1 Jn 2:2 And he is the propitiation for our sins: and not for our's only, but also for the sins of the whole world.
Christians have not cornered to market for Jesus.
It does not say if christians sin, it says "If any man sin".