The voice of the author ought to be sympathetic without patronizing the reader. It should carry a sincere gentleness which, though formal, is soft-spoken and universally welcoming. It is not (unless absolutely necessary) the mechanical rigidity of logical parsing; nor a syrupy sycophancy. It is above all, human. One thinks of Tom Bombadil from The Lord of the Rings. How does one unselfconsciously, and without the slightest self-aggrandizing, be as familiar and comfortable to the reader as a closest friend?
Once that voice is present, the same voice must also be--unselfconsciously--supremely assured about the End, about the ultimate Triumph of good. As per St. Julian of Norwich, "all will be well, and all will be well, and all manner of things will be well." This has nothing to do with being omniscient. The author should be a "gatekeeper", like Virgil to Dante. If he is not omniscient, he is at, least, trustworthy; the reader has no hard "proof" of this, and rightly so, else it would not be trust.
Like the measured morsels of truth the author slowly uncovers, the gatekeeper himself is never fully disclosed nor totally hidden. This is not a contrived "peek-a-boo" meant to manufacture a false mystique. In fiction, the "gatekeeper" archetype has a goal which stretches beyond merely transmitting information--a goal that is vulnerable to carelessness in letting too many know too much before the right time. The point is not to be frivolously coy. It is to be the midwife of a delicate labor of truth.
Another "Lord of the Rings" figure I believe exemplifies this is Gandalf. Gandalf is both personable and mysterious; both warm and elusive. He does hold his cards close to his chest, to be sure, but at the same time he communicates the unspoken assurance that his mystery, like his warmth, is ordered toward joy.
Pippin glanced in some wonder at the face now close beside his own, for the sound of that laugh had been gay and merry. Yet in the wizard's face he saw at first only lines of care and sorrow; though as he looked more intently he perceived that under all there was a great joy: a foundation of mirth enough to set a kingdom laughing, were it to gush forth.