He teaches: “Real faith is incompatible with any sin whatsoever; whoever is a believer must resist sinful lusts by the power and the impulse of the faith and Spirit.”[529] “Whoever has faith in the forgiveness of sins does not obey sinful lusts, but fights against them until he is rid of them.”[530] Where mortal sin has been committed, there, according to him, real faith was manifestly lacking; it had already been denied and was no longer active, or even present. A revival of faith, together with the necessary qualities of confidence, covers over all such sins, including the sin of unbelief. On the other hand, sins committed where faith was present, though for the moment too weak to offer resistance, were sins of frailty; there faith at once regains the upper hand and thus forgiveness or non-imputation of the sin is secured. The denial of Peter was, according to Luther, a sin of frailty, because it was merely due to “chance weakness and foolishness.” Nevertheless he declares that, like the treason of Judas, it was deserving of death.[531] Luther teaches further, affording us incidentally an insight into the inadequacy of his doctrine from another point of view, that, in the case of the heathen or of Christians who had no faith, not only was every sin a mortal sin, but also all works, even good works, were mortal sins; indeed, they would be so even in the faithful, were it not for Christ, the Redeemer, Whom we must cling to with confidence. Moreover, as we know, man’s evil inclinations, the motions of concupiscence, the bad tendencies of the pious, were all grievous sins in Luther’s eyes; original sin with its involuntary effects he considers an enduring offence; only faith, which merits forgiveness and overcomes the terrors of conscience by the saving knowledge of Christ, can ensure man against it, and the other sins.