“in the midst of the Jordan.” That is to say that there was water all around where the priests were, but they were not in the “middle” of the Jordan, which would have been the very middle of the riverbed.
“on dry ground.” The fact that God not only divided the water but dried up the ground is an important part of the miracle of the crossing of the Jordan (and the crossing of the Red Sea; cp. Exod. 14:21-22). The God who can split the waters can also dry up the land so the riverbed was dry to cross over. This is the same word as when Elijah struck the Jordan and Elijah and Elisha crossed over on dry ground (2 Kings 2:8; cp. also Gen. 7:22).
“the nation.” The Hebrew word goy is rarely used of Israel. E. Fox (The Schocken Bible) says: “Its usage here suggests that the crossing of the Jordan is an act of nation-founding.” There was also a “mixed multitude” with Israel, and this may indicate that in the Promised Land they would become more integrated with Israel, and indeed, even some Canaanites, such as Rahab, joined the nation of Israel.
During the seven years of famine that came over Egypt and Palestine, Joseph sent for his family and brought them to Egypt. Jacob must have had some concern about leaving the land God promised to Abraham and even to Jacob (Gen. 48:3-4) because God spoke to Jacob as he was starting the journey to Egypt and said, “I am God, the God of your father. Do not be afraid to go down into Egypt, for there I will make of you a great nation” (Gen. 46:3). So God promised to make Jacob a great nation in Egypt, and that came to pass. Now they enter the Promised Land as a nation.