The answer is: God stopped providing manna

Josh 5:12 - Now they enjoyed the produce of the land.

After the Israelites celebrated Passover, they experienced a significant shift in their life in the Promised Land. Remember, for years they had relied on the miraculous manna—a flaky bread-like substance that fell from the sky—to sustain them in the desert. It was their divine fast-food, arriving each morning, gathering could start a whole new day for them. Now, this reliance was dramatically changed as they feasted on the land's bounty.

This moment signifies not just a logistical shift from manna to discovering the produce of Canaan but also a profound shift in their relationship with God and their environment. God was ushering them into a new chapter of their lives—one that required cultivating the land, eating actual crops, and claiming responsibility for their sustenance. This could be seen as a metaphorical graduation; they moved from dependency to shared sustenance with God in a radically different setting—the Promised Land.

Interestingly, this transition also echoes the experience of many subsequent generations in Jewish tradition. The cycle of harvest celebrations and prayers for abundance roots back to this pivotal moment. Even the Feast of Weeks, or Shavuot, follows Easter, reinforcing how vital agriculture and community were to the Jewish identity. It illustrates how the Israelites' journey hinged not only upon their trials but also upon their ability to flourish and establish themselves practically.

Thus, this story reflects a significant evolution in their existence—a movement from reliance on divine provision to thriving through their own labor and God's blessings. It encapsulates a vital theme: transformation and the importance of growth.