Bhashya
तस्मात् प्राणो ह्येवैतानि पित्रादीनि सर्वाणि भवति च-लानि स्थिराणि च ।स वा एष प्राणविदेवं यथोक्तप्रकारेणपश्यन् फलतो अनुभवन् एवं मन्वानः उपपत्तिभिश्चिन्तयन्एवं विजानन् उपपत्तिभिः संयोज्य एवमेवेति निश्चय कुर्व-न्नित्यर्थः ।मननविज्ञानाभ्यां हि संभूतः शास्त्रार्थो निश्चितोदृष्टो भवेत् ।अत एवं पश्यन् अतिवादी भवति नामाद्या-शान्तमतीत्य वदनशीलो भवतीत्यर्थः ।तं चेद्ब्रूयुः तं ब्रह्मा-दिस्तम्बपर्यन्तस्य हि जगतः प्राण आत्मा अहमिति ब्रुवाणंयदि ब्रूयुः अतिवाद्यसीति, बाढम् अतिवाद्यस्मीति ब्रूयात्,न अपह्नुवीत ।कस्माद्धि असावपह्नुवीत ? यत्प्राणं सर्वेश्वरम्अयमहमास्मि इत्यात्मत्वेनोपगतः ॥
In plain words
Therefore prāṇa indeed becomes all these moving and steady things, from our fathers onward. Such a knower of prāṇa, seeing, experiencing the fruit, reflecting with logical proofs, and directly knowing—that is, establishing this definite conclusion through both thought and insight—becomes an ativādin, one who speaks from beyond all the categories from name to hope. When he declares that prāṇa is the Self of the entire universe from Brahmā down to a blade of grass and that he is that Self, if people ask him, 'Are you an ativādin?' he should answer, 'Yes, I am.' He must never hide it. Why would he conceal it, when he has realized the all-ruling prāṇa as his very own Self?
Close to the Sanskrit
Therefore prāṇa surely becomes all these fathers and others, moving and steady. That very knower of prāṇa, seeing in the stated manner, experiencing through the fruit, thinking through logical proofs, knowing through logical proofs—establishing certainty thus, meaning: through reflection and realization the scriptural meaning becomes ascertained and seen. Hence seeing thus, he becomes an ativādin, meaning one who speaks having transcended all ending with hope. If they should say to him—when he declares 'Prāṇa is the Self of this entire universe extending from Brahmā down to a blade of grass, I am that'—if they should say 'You are an ativādin,' he should say 'Yes, I am an ativādin,' he should not conceal it. For why should he conceal it? Since he has approached the all-ruling prāṇa as his own Self, thinking 'I am this.'