The Torah writes (Shemot 13:18) that Bnei Yisrael left Egypt "chamushim," which Rashi explains as armed with weapons. Immediately thereafter it says that Moshe took the bones of Yosef with him. The gemara (Sota 13a) relates to Moshe’s action the pasuk in Mishlei (10:8) that "the wise of the heart will buy mitzvot," as instead of acquiring spoils from Egypt, Moshe was involved in this mitzva.
As Bnei Yisrael was preparing for independence, like other nations enjoy, many made the mistake of thinking that their survival would depend on the same things it would for other nations. They left with arms, ready to assemble an army of warriors. They thus left with a "powerful hand" (Shemot 14:8). When they were accumulating the spoils that would get them off "on the right foot" economically, their leader, of all people, had other concerns. He was attending to the bones of an old deceased leader, which were buried under the Nile for many decades, a seemingly irrelevant act at this time of great immediate opportunity. While it might have been a pious act, where was the "wisdom of the heart" that the pasuk refers to?
The people found out the answer to that question a few days later. Paroh, who the people thought they had seen the last of, was attacking with a whole army of well-armed Egyptians. In one moment, the hearts of the previously confident former slaves froze in fear. The people started screaming that they would be annihilated. What happened to all the weapons they brought with them and all the plans to use them? Did they not know how to fight for their lives?
As we know, they were saved by the miracle of the splitting of the sea. But how did that happen? The midrash (Bereishit Rabba 87:8) tells us that "the sea saw and fled" (Tehillim 114:3) refers to seeing the casket of Yosef. What power did Yosef possess that so "scared" the sea?
Yosef represented the power of mesirut nefesh (the willingness to sacrifice) for Judaism. It was Yosef who resisted his temptation from Potiphar’s wife, even at the price of being put in jail. When he eventually became powerful, it was he who refused to assimilate among the Egyptians and he who wanted to be buried along with his brothers in the Land of Their Fathers. When someone needed to learn how to find the courage to jump into the raging sea, where would he find it? From the spoils he had taken from Egypt?! No, he would find it by contemplating the courage of Yosef. All of the preparations turned out to be useless, except for the inspiration provided by the remains of Yosef, which Moshe had brought. No, it was not "only" piety; Moshe’s planning was a better strategy in the long run as well.