The immediate goal is to form a "battle group" which is independent of NATO and whose goal is to provide for the defense of the four. Concerns about a resurgent Russia, a wimping-out United States, and a Germany unhappy with its European Union partners seem to be the motivating forces behind their remilitarization.
Europe is a place where world wars are incubated; perhaps we are seeing the embryonic beginnings of yet another. You'll find the source article at RealClearWorld.