First of all, we should see that the divine reaction here is that of the overshadowing purpose ,of God that is determined to have His way with His people. God is, we must remember - working to a plan, - He is involved in nothing less than the redemption of the world, and all He does must be interpreted in that light. He must correct and chastise from that over-ruling standpoint. He sees best what is good, and must discipline His people towards this, however grimly. We could take 1-3, as a brief summary of the whole issue, with 4 ff describing and elaborating the details; or, we could take the events of 1-3 as preceding those in 4 ff. Either way, it is clear that 4 ff give the substance of the problem that faced Moses (for a commentary on this, see Psalm 78:11 ff). What it amounts to is this: God had bestowed on Israel the dignity and privilege of a spiritual calling and destiny.; He had made bare His holy arm on their behalf, shown them the bright and glorious prospect that faced them if they were prepared to walk in His ways - and they jibed at it, reacted against it, lightly esteemed it, and turned their backs on their destiny, in sheer, carnal and fleshly worldliness. Discontent with a spiritual calling - this is the theme, and its relevance and importance are surely obvious for us, in relation to how He dealt with them for their sins.