After the Israelites left Egypt, God gave them a 40-year timeout in the desert. This was because of their lack of trust in his pledge to provide for them as they entered into the land he promised. This meant that what should have been an eleven day journey, ended up being a 40-year desert experience — which for most, literally lasted a lifetime.
While their desert sojourn was marked by complaining and disobedience, there were a couple of significant bookend events to their time of waiting.
First, they celebrated Passover for the first time just before they left Egypt to head to the desert. Then they celebrate it again, 40 years later after they leave the desert. The first Passover was marked by God’s provision for them to leave Egypt, while the subsequent ones were intended as a reminder of the first.
Second, two miracles occurred, allowing them to enter and later leave the desert. After leaving Egypt, and being pursued by its army, God parted the sea so they could escape attack and enter into the desert. Forty years later, when it was time to leave the desert, God parted the Jordan River — at flood stage — allowing them to leave.
So their desert experience began with Passover and the parting of the sea; it ended with the parting of another body of water and another Passover celebration.