דברים י א, ל : הֲלֹ א -ה מ ָּ ה ב ְע בֶ ר דְרַ יַהן Are they on the other side of the Yarden?
Baal HaTurim notes that the final letters of these four words spell AHaRoN. This is an allusion to the loss of Aharon. As long as he was still alive bnei Yisroel did not need specific directions, as the Clouds of Glory, which were present in the merit of Aharon, were their GPS. Now that he was gone then bnei Yisroel needed detailed directions.