John Wesley on Deuteronomy 33:28

Alone - Either Tho' they be alone, and have no confederates to defend them, but have all the world against them, yet my single protection shall be sufficient for them. Or, Distinct and separated from all other nations, with whom I will not have them mingle themselves. The fountain - That is, the posterity of Jacob, which flowed from him as waters from a fountain, in great abundance. The fountain is here put for the river or streams which flow from it, as Jacob or Israel who is the fountain is often put for the children of Israel. His heavens - That is, those heavens or that air which hangs over his land.