। ॥ ५६ ॥
In plain words
Truth is what no past, present or future can touch. Prāṇa, space, the directions and all that follows rest within it; the teaching therefore calls Brahman the truth of truth, with nothing higher beyond it. The formed and the formless make up a lower, conditioned truth, and Brahman is the reality by which even that is true.
Close to the Sanskrit
That which remains uninjured through past, present and future is truth. Prāṇa, the directions, space and the rest abide at rest in it; therefore Brahman is declared here to be the truth of truth. Nothing higher or greater exists, hence the name. The formed and the unformed, conditioned by form and the rest, are the lower truth; Brahman is the truth even of these.