In plain words
Whatever is the seed of all beings—that too am I, Arjuna. There is no moving or unmoving being that can exist without Me.
Word for word
And whatever also is the seed of all beings, that [am] I, O Arjuna; there is not that being, moving or unmoving, which would be without Me.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
यच्चापि सर्वभूतानां बीजं प्ररोहकारणम् , तत् अहम् अर्जुन । प्रकरणोपसंहारार्थं विभूतिसङ्क्षेपमाह — न तत् अस्ति भूतं चराचरं चरम् अचरं वा, मया विना यत् स्यात् भवेत् । मया अपकृष्टं परित्यक्तं निरात्मकं शून्यं हि तत् स्यात् । अतः मदात्मकं सर्वमित्यर्थः ॥ ३९ ॥
In plain words
And whatever is the seed of all beings, the cause from which they sprout — that too is what I am, Arjuna. To bring the section to a close, he sums up the whole range of manifestations in a single stroke: there is no being at all, moving or unmoving — nothing that walks, nothing that stands still — that could exist apart from me. Draw it away from me, let it go entirely, and it would be left with no self in it, sheer emptiness. So everything has me for its very self. That is the meaning.
Close to the Sanskrit
And whatever is the seed of all beings, the cause of their sprouting — that I am, Arjuna. In order to conclude the section, he states the summary of the manifestations: there is not that being, moving or unmoving — moving, or unmoving — which could exist without me. For withdrawn from me, abandoned, it would be without self, void. Therefore everything has me as its self — this is the meaning.