“It is a Shabbat for H’Shem, in all your dwelling places.” – Leviticus 23:3
Why does the Torah specify, “In all your dwelling places?” Ibn Ezra comments, “In your country and outside of your country, at home and on the way” (sefaria.org). Sforno writes, that the specification “indicates that the commencement and conclusion of the Sabbath depends on the local times of day and night, not on a central location” (sefaria.org). And, Chizkuni notes that “The Sabbath laws apply regardless of whether you are in the Holy Land or in exile” (sefaria.org). Within the framework of this line of reasoning, the Sabbath, as Abraham Heschel points out, is a time designation, regardless of place.
Therefore, whereas the moadim are mentioned in the previous verse, some significance can be understood, in regard to the Sabbath. Perhaps, it is as if to imply, that on the moadim, when you travel to Jerusalem, to observe the shalosh regalim, three holidays in Jerusalem, these are considered Sabbaths, and must also be observed as Shabbat, outside of Jerusalem, as well, for all who are unable to make the journey to Jerusalem.
This would have relevancy, in particular, to the Jews living outside of Israel, after the dispersions, beginning with the Babylonian exile, as well as the Roman exile. Furthermore, this has primary relevance for us today, as well. For, only in Jerusalem, do the moadim become holidays observed in both time and place, according to Torah. Even though we observe, for the most part, these holidays in the synagogue today, this was not the original intention, and is only a modern substitute, in lieu of all of the Yehudim being gathered back into Israel. Yet, when Moshiach reigns from Jerusalem, we may all observe the holidays in time and place.