'First Day' in the Bible

On the first day you shall have a holy convocation (calling together); you shall not do any laborious work [on that day].

“Say to the children of Israel, ‘On the first day of the seventh month (almost October), you shall observe a day of solemn sabbatical rest, a memorial day announced by the blowing of trumpets, a holy convocation.

The first day is a holy convocation (calling together); you shall not do any laborious work [on that day].

‘On exactly the fifteenth day of the seventh month (nearly October), when you have gathered in the crops of the land, you shall celebrate the feast of the Lord for seven days, with a Sabbath rest on the first day and a Sabbath rest on the eighth day.

Now on the first day you shall take for yourselves the foliage of beautiful trees, branches of palm trees, and boughs of thick (leafy) trees, and willows of the brook [and make booths of them]; and you shall rejoice before the Lord your God for seven days.