ॐ इत्येतदक्षरमिदं सर्वं तस्योपव्याख्यानं भूतं भवद् भविष्यदिति सर्वमोङ्कार एव यच्चान्यत् त्रिकालातीतं तदप्योङ्कार एव ॥ १ ॥
In plain words
Om is all this. Its clear explanation is: what was, what is, and what will be—all is Om. Whatever else transcends the three divisions of time is also Om.