The use of the and before the main clause seemed inappropriate to the 1830 typesetter, so he omitted it from the text. It is possible that Oliver Cowdery, the scribe in 𝓞, accidentally inserted the extra and. He could have been influenced by the and in the immediately preceding predicate (“and went forth to the tent door”), although independent evidence for Oliver making this kind of scribal error is virtually nonexistent.
Another possibility is that the and here represents a Hebraism in the text—namely, the use of and to connect a main clause to a preceding subordinate clause. In this case, the subordinate clause begins with the subordinate conjunction as (“as my father arose in the morning and went forth to the tent door”). For another example involving as, see 1 Nephi 8:13. (For a complete discussion and a list of examples, see hebraisms in volume 3.) Since this Hebraistic use of and appears to be intended, the critical text will restore such and ’s whenever they are supported by the earliest textual sources.
Summary: Restore in 1 Nephi 16:10 the Hebraistic and that connects the main clause with the preceding as-clause.