Matthew Poole and continuators on Acts 2:1

ANd when the day of Pentecost was fully come, they were all with one accord in one place.

This feast was fifty days after the feast of unleavened bread or Passover, as Levit. 23.16. whence it had its name, and was called the feast of weeks, Exod. 34.22. because it was to be observed seven weeks after the feast of unleavened bread, Deut. 16.9. It was the feast of the first fruits of wheat Harvest, Exod. 34.22. and on this day (to answer the Type) the spirit was poured out in such a plentiful manner, as the first fruits of Christ's Ascending into Heaven; besides, the Law was given on this day, Exod. 19.1, 11. and 'twas expedient that the Gospel (Christs Law) should be published on the same day: and it being on the first day of the week, it did recommend and honour the Lords day, as our Saviour had before by his Resurrection on that day.

As if they had but one mind, as sent in so many bodies in one place; probably, that mentioned Chap. 1.13.