In plain words
Once one has attained completeness, what happens to man's very condition? — many may ask, or wonder. His life, once it has attained fullness, shines forth complete, full of unsurpassed bliss. In that oneness too, he experiences the infinitude of God, the one entity fit to be the source of happiness for life. True happiness is that alone. God alone is the eternal embodiment of happiness. All Bharatiyas — that is, all the various schools of thought among them — follow this very doctrine, and take up this very tenet as their own.
'The principle of completeness' means, of course, the indivisible principle. The indivisible principle is one alone; there cannot be two or three, can there! Individuality too cannot exist, can it! One might object: once a jīvātma has become completeness and indivisibility itself, it would no longer be possible for it to make this known to the world again, would it? — one might well suspect so. But this is not a correct view. When the jīva takes on the universal form, its sense of individual distinction vanishes and the universal state comes about. Then it comes to realize that the essence of all things is one alone — but it does not thereby assert any individual distinctness. The divinity within each single thing, recognizing that very principle of the Ātma within itself, rejoices all the more, but it does not proclaim any difference. The very rays of that bliss spread everywhere, and others receive that experience. The great ṛṣis