Scribe 3 of 𝓞 initially wrote the impossible ceathes, then immediately corrected it to ceases. But Oliver Cowdery, in copying from 𝓞 into 𝓟, wrote ceaseth. There is good evidence that Oliver’s interpretation is correct, rather than the other possibility, ceases. Scribe 3 probably heard the th at the end of the word, which resulted in his metathesized spelling ceathes instead of ceaseth. When he corrected his mixed-up spelling, he overwrote the th to s (with heavier ink flow) but neglected to change the final s to th. It is also possible that Joseph Smith found it difficult to dictate “ceaseth soon” to his scribe. This pronunciation difficulty (a real tongue twister) could have contributed to the confusion.
Usage elsewhere in the text supports the choice of ceaseth; in fact, there are no examples of ceases elsewhere in the text, only ceaseth. And the first of these examples expresses the same idea as 1 Nephi 7:14:
Summary: Even though 1 Nephi 7:14 ultimately reads ceases in the original manuscript, it was originally written as ceathes, which implies that the intended reading was ceaseth; this form is the one used consistently elsewhere in the text.