Matthew Poole and continuators on Leviticus 23:39

39 Also, in the fifteenth day of the seventh moneth, when ye have gathered in the fruit of the land, ye shall keep a feast unto the LORD seven dayes. On the first day shall be a sabbath, and on the eighth day shall be a sabbath.

Or, rather surely, as this particle is oft used: For this is no addition of a new, but onely a repetition of the former, injunction, with a more particular explication both of the manner and reason of the feast.

Not the corn, which was gathered long before, but of their trees, as vines, olives, and other fruit-trees: which compleated the harvest, whence this is called the feast of in-gathering, Exod. 23. 16.