In the sixteenth verse, Arjun had said that the form of the Lord is without beginning, middle, or end. He repeats this after just three verses, out of his excitement over what he is seeing. If a statement is uttered repeatedly in amazement, it is taken as an expression of wonder and not considered a literary flaw. For example, on seeing a snake, one may scream, “Look, a snake! A snake! A snake!” Similarly, Arjun repeats his words in amazement.
God is indeed without a beginning and end. That is because space, time, and causation are within him. So he is beyond the measure of their limits. He cannot be encompassed either by space, time, or causation. Further, the sun, moon, and stars receive their energy from the Lord. Thus, it is he who provides warmth to the universe through these entities.