If the soul is left in darkness, sins will be committed. The guilty one is not he who commits the sin, but he who causes the darkness.
 
[Cette âme est pleine d’ombre, le péché s’y commet. Le coupable n’est pas celui qui y fait le péché, mais celui qui y a fait l’ombre.]

Victor Hugo (1802-1885) French writer

Les Misérables, Part 1 “Fantine,” Book 1 “An Upright Man,” ch. 4 (1.1.4) [Bishop Myriel] (1862) [tr. Wilbour (1862)]
    (Source)

(Source (French)). Alternate translations:

This soul is full of darkness, and sin is committed, but the guilty person is not the man who commits the sin, but he who produces the darkness.
[tr. Wraxall (1862)]

This soul is full of shadow; sin is therein committed. The guilty one is not the person who has committed the sin, but the person who has created the shadow.
[tr. Hapgood (1887)]

The soul in darkness sins, but the real sinner is he who caused the darkness.
[tr. Denny (1976)]

If the soul is left in darkness, sins will be committed. The guilty one is not he who commits the sin, but the one who causes the darkness.
[tr. Wilbour/Fahnestock/MacAfee (1987)]

In any benighted soul -- that's where sin will be committed. It's not he who commits the sin that's to blame, but he who causes the darkness to prevail.
[tr. Donougher (2013)]