It was only after a year in the Midbar, that the Bnei Yisrael were counted in order to be set up under the Degalim, where each Shevet was given their own flag. Why did Hashem wait so long to give them this mitzva?
Rav Yaakov Kaminetzky (Emes L'Yaakov) says that in principal creating the Degalim was a dangerous move. By dividing up a group of people with each one having their own banner and motto, competition could evolve with feelings of nationalism. However, if all of the groups have the same goal, and each contribute to the cause in their own unique way, this danger doesn't exist. The eyes don't compete with the ears since their roles are different. This way various factions can work together towards their mutual goal.
The Mishkan was only put up in Nissan of the second year. Hashem wanted to wait for the Degalim until the Avodas HaMishkan become the focal point of life in the Midbar. Only then, was it safe to give a clear identity to each Shevet. That is why the pasuk says (Bamidbar 2:2), "Ish Al Diglo B'Osos L'Bais Avosam... Saviv L'Ohel Moed Yachanu," only when their lives revolved around the Mishkan did Hashem divide them up and give them each their own specific mission.
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