“And this is of Judah: and he said,
Hear, Yahweh, the voice of Judah,
And bring him in to his people.
With his hands he contended for himself;
And you will be a help against his adversaries.”
Judah would tend to be a loner but must be welcomed as part of the greater confederacy. Moses was aware of the trend for them to keep separate apart from their special relationship with Simeon, a trend already evident, and prayed that Yahweh would continue to ‘bring him in to his people' so that they did not break away completely. As a proud tribe they did later stand almost alone, which they could do because of their great size and power, which would already have been evident at this stage. This was seemingly apparent to Moses from the beginning, for he set them in the vanguard of the advance (Numbers 2:9). They will tend to stand on their own, he declares, and will triumph with God's help. But they would still need Yahweh's help against their adversaries.
Jacob had already declared that Judah would bear the sceptre, (Genesis 49:10 - see Genesis 43-44 where he had already established his leadership among the sons of Jacob) and would thus be a royal tribe. But Moses says nothing of this, which is evidence of the early date of the poem. There was no kingship other than Yahweh's on the horizon at this point in time.
The shortness of the blessing comes as something of a surprise in comparison with Genesis 49. This may partly be because Simeon was seen as coming under their umbrella because Simeon's own chieftainship had been shamed at Baal-peor, with the thought that the least mentioned the better.