Exodus 13 is about the establishment of an annual festival, celebrating what the Lord did for the Israelites, "with the power of His mighty hand, the Lord brought us out of Egypt". Part of the annual event would include the dedication of every firstborn among the Israelites to the Lord, so in this way they would always remember how the Lord had rescued them from their slavery in Egypt. When they left, Moses brought the bones of Joseph, since Joseph had said "God will certainly come to help you. When he does, you must take my bones with you from this place." When the Israelites left, "the Lord went ahead of them and guided them" leading them day and night through the wilderness.