Imitation of Christ

Si tu esses intus bonus, et purus, tunc omnia sine impedimento, et caperes bene. Cor purum penetrat cælum, et infernum. Qualis unusquisque est intus, taliter iudicat exterius. Si est gaudium in mundo, hoc utique possidet cordis puri homo. Et si est alicubi tribulatio et angustia, hoc melius novit mala conscientia. Sicut ferrum missum in ignem amittit rubiginem et totum candens efficitur, sic homo ad Deum integre se convertens, a torpore exuitur, et in novum hominem transmutatur. 

If you were good and pure within, then you would look upon all things without hurt and understand them aright. A pure heart sees the very depths of heaven and hell. Such as each one is inwardly, so he judges outwardly. If there is any joy in the world surely the man of pure heart possesses it, and if there is anywhere tribulation and anguish, the evil conscience knows it best. As iron cast into the fire loses rust and is made altogether glowing, so the man who turns himself altogether unto God is freed from slothfulness and changed into a new man.

Imitation of Christ, II, 4:2