The best way to understanding is a few good examples.

Nature does nothing in vain when less will serve; for Nature is pleased with simplicity and affects not the pomp of superfluous causes.

Every action has an equal and opposite reaction

Every body persists in a state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces having impact upon it.

If I have ever made any valuable discoveries, it has been due more to patient attention, than to any other talent

Our present work sets forth mathematical principles of philosophy. For the basic problem of philosophy seems to be to discover the forces of nature from the phenomena of motions and then to demonstrate the other phenomena from these forces. It is to these ends that the general propositions in books 1 and 2 are directed, while in book 3 our explanation of the system of the world illustrates these propositions.

If two angels were sent down from heaven -one to conduct an empire and the other to sweep the streets -they would feel no inclination to change employment because an angel would know that no matter what we are doing, it's an opportunity to bring joy, deepen our understanding and expand our life.