C. S. Lewis' helpful essays 'The Poison of Subjectivism' is as relevant today as it was in the post WWII days when he wrote it, as well as being an example of the way Lewis helps us simply to think. Here's one passage in which he answers the charge that 'traditional morality' and an objective understanding of good and evil 'exclaims that to tie ourselves to an immutable moral code is to cut off all progress and acquiesce in "stagnation."' Lewis writes:
'Let us strip [this argument] of the illegitimate emotional power it derives from the word "stagnation" with its suggestion of puddles and mantled pools. If water stands too long it stinks. To infer thence that whatever stands long must be unwholesome is to be the victim of metaphor. Space does not stink because it has preserved its three dimensions from the beginning. The square on the hypotenuse has not gone moldy by continuing to equal the sum of the squares on the other two sides. Love is not dishonored by constancy, and when we wash our hands we are not seeking stagnation and "putting the clock back". . . . For the emotive term "stagnant" let us substitute the descriptive term "permanent." Does a permanent moral standard preclude progress? On the contrary, except on the supposition of a changeless standard, progress is impossible. If good is a fixed point, it is at least possible that we should get nearer and nearer to it; but if the terminus is as mobile as the train, how can the train progress towards it? . . . We can go on getting a sum more and more nearly right only if the one perfectly right answer is "stagnant."'
--Christian Reflections (Eerdmans 1967), 76