Sentence length is pacing, and a component of rhythm, and sets up subtle expectations, whether for more of the same or something different. After three long sentences, a short and simply declarative one produces a certain affect, and feels good, rhythmically. But breaking the pattern and changing the rhythm also changes the emphasis, and (as I hear it) gives those words a higher level of significance than the more purely descriptive words and phrases of the previous sentences. Their meaning changes, however subtly. And if a change in rhythm brings about a change in meaning, then rhythm or clarity is not an either/or question.
In this case, I think the best solution would be to use a dash instead of a period, and keep it one sentence. This would let you retain most of the emphasis effect of the four single-syllable words at the start of the sentence, without creating a grammatical issue. You could accomplish similar with a semicolon, but it lacks the urgency of the dash (at least in part because it's less visually dramatic), and doesn't visually set off the words that follow. It might also feel a little "stuffy" in what seems like a relatively "poetic" context.
If you wanted to keep it two sentences, then (again to my ear), the word 'Only' feels too rhythmically soft to begin a new sentence following that short one, and so you might consider changing it to 'Just', which has a harder tone, and would better work as a bridge between the crispness of the previous words, and the longer, slower pace that returns for the rest of the sentence. It's still grammatically questionable, but that might be easier to buy if the rhythm and sound of the words help justify it.