what kind of faith

"Justification is by faith alone but not by a faith that is alone." The only kind of faith that saves is what [Martin] Luther called a fides viva - a living faith, a vital faith, a faith that issues forth in works as the fruit of faith. Those works don't count toward justification - only the merit of Christ counts toward that - but without the flowing forth of the fruit of faith, there would be no true faith in the first place. ~ RC Sproul, Defending your Faith