While Catholics acknowlege that living life without mortally sinning requires a special grace from God, Catholics do not believe that this assurance is guaranteed through faith alone, no matter what a person does. There are many biblical references that support that one can sin their way out of salvation. First and foremost is that Adam and Eve were able to sin their way out of the garden of eden. If that was the reality in the beginning, why would God “change” (a violation of immutability) to not allow it in the New Covenant?