What does it mean to live in harmony with natural law? It means that nature has taken billions of years to test and try, has gone through countless permutations in order to arrive at the best it could get. If we, as humans, understand this and align ourselves with it, life will be so much easier.
Electricity is a perfect example: we don't really know how it works, but if we touch a live wire, we know what happens to us - the discharge is going to knock us out or dead. However, if we use it in a modest and channeled form, it will provide us with all the amenities or luxuries we have created out of the pure force/potential by transforming it down to suit our needs
So the first action is not in harmony, whereas the second one is. One we cannot deal with, the other one we can. One is anti-life, the other one pro-life.
We as humans know whether we operate in harmony with natural law, when things flow, when there is no resistance, when beautiful things flourish and enrich our lives, when there is peace and harmony and a general well-being.
Nature has a wonderful way of nudging us in the right direction, because the longer we are "out of harmony with natural law", we see a widening gap between where we are and where we ought to be. This widening gap causes ever more tension and stress, a clear indicator that we are on the wrong track with our thoughts, feelings and deeds. The more in alignment we are, the more the tension eases, the more power we have for our growth rather than our mere survival and sustenance.
So, there you have it. 🙂