I have taken the Levites. The actual separation of Levi had been already anticipated (see Numbers 1:47, Numbers 1:53), but the meaning and purpose of that separation is now formally declared, into reason, however, is assigned for the choice of this particular tribe.
It is almost always assumed that their zeal in the matter of the golden calf was the ground of the preference shown to them now. But it may be doubted whether there was any "preference" in the matter at all.
To Aaron and his seed on undoubted and important preference was shown, but the functions and position of the Levites were not such as to give them any preeminence, or to secure them any substantial advantage.
They were tied down to the performance of routine duties, which demanded no intelligence, and gave scope for no ambitions. The one obvious reason why Levi was selected is to be found in the fact that he was by far the smallest in numbers among the tribes, being less than half the next smallest, Manasseh, and almost exactly balancing the first-born.
A larger tribe could not have been spared, and would not have been needed, for the purpose in question. If any more recondite motive must be sought for the Divine selection, it must be found in the prophecy of Genesis 49:7.
Levi as well as Simeon, though in a different way, was doomed never to raise his head as a united and powerful tribe among his brethren.