In plain words
And why should they not bow to You, great One, You who are greater still, the primal Creator even of Brahma? Infinite Lord, God of gods, abode of the universe, You are the Imperishable, beyond both being and non-being.
Word for word
And why should they not bow to You, O great-souled one, the greater, the first creator even of Brahmā? O infinite one, O Lord of gods, O abode of the world, You [are] the imperishable, being and non-being, that which [is] beyond.
The commentators
Bhagavadgītābhāṣyam
भगवतो हर्षादिविषयत्वे हेतुं दर्शयति —
कस्माच्च हेतोः ते तुभ्यं न नमेरन् नमस्कुर्युः हे महात्मन् , गरीयसे गुरुतराय ; यतः ब्रह्मणः हिरण्यगर्भस्य अपि आदिकर्ता कारणम् अतः तस्मात् आदिकर्त्रे । कथम् एते न नमस्कुर्युः ? अतः हर्षादीनां नमस्कारस्य च स्थानं त्वं अर्हः विषयः इत्यर्थः । हे अनन्त देवेश हे जगन्निवास त्वम् अक्षरं तत् परम् , यत् वेदान्तेषु श्रूयते । किं तत् ? सदसत् इति । सत् विद्यमानम् , असत् च यत्र नास्ति इति बुद्धिः ; ते उपधानभूते सदसती यस्य अक्षरस्य, यद्द्वारेण सदसती इति उपचर्यते । परमार्थतस्तु सदसतोः परं तत् अक्षरं यत् अक्षरं वेदविदः वदन्ति । तत् त्वमेव, न अन्यत् इति अभिप्रायः ॥ ३७ ॥
In plain words
And here is exactly why you are the fitting object of all that joy —
How, O great soul, could they not bow to you — to one more venerable than any other, greater than all? Because you are the very source even of Brahmā, the maker of the maker himself, the first cause of everything. How could they not bow? You alone are the true, fitting place for all joy, all homage — that is simply the truth of it. O boundless one, Lord of the gods, home of the whole world, you are the Imperishable, that supreme reality the scriptures speak of. What is it, exactly? It is called 'being and non-being.' Being is whatever exists; non-being is only the thought 'this is not here.' Both of these are merely surface markers laid over the true Imperishable — through them, people speak of it as 'being and non-being,' but only in a manner of speaking. In ultimate truth, the Imperishable stands beyond both being and non-being altogether — that is what those who know the Veda are really pointing to. And that reality is you. Nothing else. That is exactly what this means.
Close to the Sanskrit
He shows the reason for the Lord's being the object of joy and the rest —
And for what reason should they not bow to you, O great soul, to the more venerable one, to the greater one; because you are, even of Brahmā, of Hiraṇyagarbha, the original creator, the cause — therefore, for that reason, to the primal creator. How could these not bow? Therefore, you are the fitting place, the fitting object, of joy and the rest and of homage; such is the meaning. O infinite one, Lord of the gods, O abode of the world, you are the Imperishable, that supreme reality, which is heard of in the Vedānta texts. What is that? 'Being-and-non-being,' thus. Being is the existent; non-being is the notion 'it does not exist here' — those two, being and non-being, serving as adjuncts of which Imperishable, through which it is figuratively termed being-and-non-being. But in ultimate reality, that Imperishable which is beyond being and non-being, that Imperishable the knowers of the Veda declare. That is you alone, not anything else — such is the intended meaning.