Interior or spiritual solitude is not to be confounded with physical or personal solitude. It is something more, and something higher, than mere seclusion of the body in some hidden or remote place.
In the accounts of those, who, in the early periods of Christianity, retired into solitary places, with the object of perfecting their inward state in desolate caverns, in forests, and in the seclusions of monasteries, we find frequent mention of unexpected and heavy temptations. Often did the world, in the shape of evil desires and vain imaginations, follow them to their lonely retreats. It is related of St. Jerome, whose devout writings still edify the church, that, in the ardor of his young piety, he thought he could successfully escape the temptations of luxurious cities, and perfect his inward experience, by dwelling alone in the solitary deserts of Syria. In the midst of those vast plains, scorched by the burning sun, he sat down alone, emaciated, disfigured, with no companion but wild beasts. Strong were his resolutions; great were his sufferings; many were the penitential tears which he shed; — but, in the midst of this desolation and of these flowing tears, he informs us that his busy imagination placed before him the luxuries of Rome and the attractions of her thoughtless voluptuaries, and renewed the mental tortures which he hoped he had escaped. [See Pantheon Litteraire. Œuvres de St. Jerome.]
To be secluded, therefore, in body is not enough. To be alone in caves and in forests is not necessarily to be alone with God.
— edited from A Treatise on Divine Union (1851) Part 6, Chapter 10.