He does so with the aid of Polaroid photos and many notes, some of which are tattooed on his body. If it's in his handwriting, he acknowledges it as true and acts as if it is true from there on. It's not exactly non-linear, but it is certainly told in an unusual fashion. Pilate may have asked the key question. Generally however, it has a metaphysical use with a practical spiritual end.
Truth is reality in relation to the vital interests of the soul.
Truth exists more in how we live, than in what we think of as facts. He brings harmony to a disordered world. Truth is not discerned intellectually, it is discerned spiritually. From the death of the old the new proceeds, And the life of truth from the death of creeds. I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.