139 Relying therefore solely on the all-powerful aid of Him "Who wishes all men to be saved," let us strive with all our strength to help those unhappy souls who have turned from God and, drawing them away from the temporal cares in which they are too deeply immersed, let us teach them to aspire with confidence to the things that are eternal. Sometimes this will be achieved much more easily than seems possible at first sight to expect. For if wonderful spiritual forces lie hidden, like sparks beneath ashes, within the secret recesses of even the most abandoned man - certain proof that his soul is naturally Christian - how much the more in the hearts of those many upon many who have been led into error rather through ignorance or environment.
Source: Quadragesimo Anno (Vatican.va)