स यथोर्णनाभिस्तन्तुनोच्चरेद्यथाग्नेः क्षुद्रा विस्फुलिङ्गा व्युच्चरन्त्येवमेवास्मादात्मनः सर्वे प्राणाः सर्वे लोकाः सर्वे देवाः सर्वाणि भूतानि व्युच्चरन्ति तस्योपनिषत्सत्यस्य सत्यमिति प्राणा वै सत्यं तेषामेष सत्यम् ॥ २० ॥
In plain words
Picture a spider stepping out along its own thread — or the countless small sparks that leap from a fire in every direction. That is exactly how everything comes out of this Self: every breath of life, every world, every god, every creature there is. Its secret name is 'the truth behind the truth': the breaths of life are called real — and this Self is what makes even them real.
Close to the Sanskrit
Just as a spider comes out by means of its thread, and just as tiny sparks fly forth in every direction from fire, so exactly, from this Self, spring forth all the vital breaths, all the worlds, all the gods, all beings. Its hidden name is 'the truth of the truth': the vital breaths are the truth, and this [Self] is their truth.