R. Yehudah Prero says: This custom of old is discussed in a number of places. The Sefer Ohev Yisroel writes there is a custom, the first Shabbos after Pesach, to pierce the Shabbos challah, the loaves, with a key. One reason for this stems from events that occurred in the days after Yehoshua (Joshua) took over the leadership of the nation of Israel. Sefer Yehoshua (5-11,12) states: “and they ate of the old grain of the land on the next day after Pesach, unleavened cakes, and parched grain in the same day; and the manna ceased on the next day after they had eaten of the old grain of the land; nor did the people of Israel have manna any more; but they ate of the fruit of the land of Cana’an that year.”
Not long after entering the land of Israel, at the time of Pesach, the nation of Israel was no longer provided with manna from heaven. The nation began to eat from that which grew naturally in the land of Cana’an, the land of Israel. At that point, the nation of Israel had to depend on G-d for the provision of sustenance in a new fashion. Until now, it had been miraculous. Now, each person had to labor and toil and work the land so that their families would be provided for. Sustenance was on the minds of everyone.
There is a metaphorical description of that place in heaven from where blessings come. G-d’s blessings, such as health and wealth, are stored behind gates. On the high holidays, we ask G-d to open the gates of heaven for our prayers. At this time of year, right after Pesach, we ask G-d to recall how He opened the gates of sustenance for the entire nation of Israel in the days of Joshua after Pesach. By impressing a key into our challah, we are asking that we too should have the key we need to open the gates of sustenance properly placed and turned for us. The “schlissel,” which is the Yiddish word for “key,” should unlock the gates of sustenance for us just as it was for the nation of Israel after their first Pesach in the promised land.
Our entry into the land of Israel brought our nation into a new status. We now had to work for our livelihoods, and our success would not come without divine providence. Whereas the divine providence had been outward and miraculous, now it would be more covert, hiding under the cover of what we term “nature.” With Yom Ha’Atzmaut, Israeli Independence Day, before us, this is a lesson to keep in the forefront. Just as our initial entry into the land of Israel brought the nation of Israel to a new level of appreciating divine providence, so too should the events surrounding the birth of the nation of Israel. Some events were clearly miraculous, others appeared to be natural. Regardless of how the events played out, we must remember, be thankful, appreciate, and pray for the continuance of G-d’s heavenly assistance, in sustaining us as individuals and a nation, physically and spiritually.