John Calvin Commentary Acts 1:12

"Then returned they unto Jerusalem from the mount called Olivet, which is nigh unto Jerusalem, a Sabbath day`s journey off." — Acts 1:12 (ASV)

To move on to another account, he shows that the disciples, having returned to Jerusalem, lived together in one room. For it was the upper part of the house, which was usually rented out to those who hired houses, as the most convenient places were reserved for the masters of the house (for their own use). Therefore, by this word, Luke signifies that they were confined to a narrow room; and yet, despite this, and though the convenience of separating would have been great, they did not separate.

They could have been more comfortably apart, yet they were not to part company before they had received the Spirit.

The fact that he notes the distance of the place here adds credibility to the account. Unless, perhaps, he meant by this to declare that they were not terrified by any fear of danger, but that they all returned and stayed together in one house. This house was not so large, and the group being larger than the place could comfortably hold might have caused some talk (or noise).

A Sabbath day’s journey was two miles, and that account agrees well with John 11:18, where it says, that Jerusalem was distant from Bethany almost fifteen furlongs; (John 11:18), which is about one thousand nine hundred paces. And the Mount of Olives was beside Bethany.

There was no Sabbath day’s journey prescribed in the Law, for the Lord simply commands them in the Law to rest on the Sabbath day. But because the Jews could not easily be governed and would go about their business on the Sabbath day (as the Lord Himself complains, that they did bear burdens out at the gates, (Jeremiah 17:24)), it is therefore thought that the priests determined (in order to restrain such grave offenses) that no one should travel on the Sabbath day more than two miles.

Although Jerome, in his Answers to Algasia, says that this tradition came from two Rabbis, namely, Atriba and Simon Heli.