It seems to me these passages are talking about the same thing. Morality is that which directs our impulses when those impulses conflict. Morality helps guide choice and action.
C. S. Lewis on Instincts and the Moral Law
[S]ome people wrote to me saying, ‘Isn’t what you call the Moral Law simply our herd instinct and hasn’t it been developed just like all our other instincts?’ Now I do not deny that we may have a herd instinct: but that is not what I mean by the Moral Law. We all know what it feels like to be prompted by instinct—by mother love, or sexual instinct, or the instinct for food. It means that you feel a strong want or desire to act in a certain way. And, of course, we sometimes do feel just that sort of desire to help another person: and no doubt that desire is due to herd instinct. But feeling a desire to help is quite different from feeling that you ought to help whether you want to or not. Supposing you hear a cry for help from a man in danger. You will probably feel two desires—one a desire to give help (due to your herd instinct), the other a desire to keep out of danger (due to the instinct for self-preservation). But you will find inside you, in addition to these two impulses, a third thing which tells you that you ought to follow the impulse to help, and suppress the impulse to run away. Now this thing that judges between two instincts, that decides which should be encouraged, cannot itself be either of them. You might as well say that the sheet of music which tells you, at a given moment, to play one note on the piano and not another, is itself one of the notes on the keyboard. The Moral Law tells us the tune we have to play: our instincts are merely the keys. (C. S. Lewis, Mere Christianity, pp. 9-10)
David B. Wong on Morality and Natural Drives
This intrapersonal function of morality comprehends what has been called “the ethical,” as opposed to what might be called the “narrowly moral.” Morality in the broader sense used here comprehends the ethical. This part of morality helps human beings to structure their lives together in a larger sense, that is, not just for the sake of coordinating with each other but also for the sake of coordination within themselves. Because the natural drives of human beings are diffuse and general, and because they are diverse and are liable to come into conflict with each other, there is a need for a shaping of these drives, and much of it comes from people telling each other just how these drives should be shaped and how internal conflicts should be regulated and resolved. (David B. Wong, Natural Moralities, p. 43)