The Hebrew term "Chol HaMo'ed (חול המועד)" refers to the intermediate, non-holy days of a biblical festival. Only the festival of Unleavened Bread and the festival of Sukkot contain such days. The feast of Unleavened Bread is a seven day festival. The Torah designates the first day and the seventh day as days of holy convocation on which work is prohibited. The intervening five days are chol HaMo'ed, intermediate days. They are not festival Sabbaths or holy convocations, but they are still part of the festival.
The term chol HaMo'ed (חול המועד) means "non-sacred [days] of the appointed time." The intermediate days are "non-sacred" only when contrasted against the days of holy convocation on which work is prohibited. Intermediate festival days still retain the sanctity of the festival season and the special commandments of the festival. For example, the Torah forbids leaven through all seven days of Passover, and it requires the native-born Israelite to live in a sukkah for all seven days of the festival of Sukkot. Nevertheless, the intermediate days of those festivals are less sacred than the days of holy convocation because the Torah permits us to work on them.
Outside of the land of Israel, traditional Judaism doubles the festival Sabbaths—a vestige from an era of calendar uncertainties. The doubling of the holy days reduces the number of intermediate days by one. Many Messianic believers, however, do not follow the Diaspora custom of doubling holy days.
A regular seventh-day (Saturday) Sabbath that falls on a day of chol HaMo'ed is called Shabbat Chol HaMo'ed. Shabbat Chol HaMo'ed is not really chol (non-sacred); instead, the holiness of the Sabbath sanctifies it. We regard it as non-sacred only in respect to the appointed time, but the holiness of the weekly Sabbath is greater than the holiness of the festivals.
For Shabbat Chol HaMo'ed Pesach, the sages assigned the Torah portion of Exodus 33:12-34:26. The Maftir is Numbers 28:19-25, and the haftarah is Ezekiel's vision of the dry bones:
"On the Sabbath which falls in the intermediate days of the festival [of Passover], the passage we read from the Torah [is the one that begins in Exodus 33:12], "See, You say to me ..." and the haftarah is the "dry bones." (b.Megillah 31a)
In addition, synagogue custom includes a public reading of Solomon's Song of Songs on Shabbat Chol HaMo'ed.
In the haftarah portion, Ezekiel describes his vision of a valley filled with dry bones. The LORD asks him if the bones can live again? Ezekiel does not know. The LORD tells him to prophesy to the bones and to the wind, telling the bones to grow bodies and the wind to return breath to the bodies. Ezekiel does, and the bones come back to life. The LORD tells Ezekiel that, in the future, He will unlock the graves of His people and bring them back to life and return them to the land of Israel. Then they will know that God is the LORD.
Why did the sages assign Ezekiel's vision of the dry bones for Shabbat Chol HaMo'ed? Rashi cites a rabbinic folk tale about a failed exodus from Egypt that the tribe of Ephraim attempted thirty years before Moses returned from Midian. All the Ephraimites that tried to leave Egypt early died in the attempt, and the valley of dry bones that Ezekiel saw was a repository of their remains. On some occasions, the sages did choose haftarah portions on the basis of folk tale and legendary associations. Another rabbinic opinion cites a tradition that the resurrection of the dead will take place in the month of Nisan. Therefore, the synagogue reads the classic resurrection text as a rehearsal for the event.
From an apostolic perspective, the reading cannot be separated from the historical recollection of our Master's resurrection. Depending on how one reckons the chronology of Yeshua's passion week, the Saturday after his crucifixion coincided with either the first day of Unleavened Bread or Shabbat Chol HaMo'ed. In either case, the first Sabbath to fall within the seven days of Unleavened Bread is the anniversary of our Master's sojourn in the grave. According to Matthew 28:1, He rose from the grave that Saturday night, as the Sabbath concluded and the first day of the week began.
Is it possible that the annual recitation of Ezekiel 37:1-14 is yet another footprint the early believers left behind in Jewish tradition? Perhaps they adopted the dry bones passage for Shabbat Chol HaMo'ed Pesach to honor the Master's resurrection and the custom spread into broader Judaism.