After reading everyone’s answers, I find it very interesting. Domestic commentators previously commented on this with remarks such as "Newton had an ideological crisis in his later years."
In fact, there is no crisis in Newton’s thinking, it is normal. Einstein and Hawking both made similar remarks, and this is no accident. Because they all know very well that attributing the first driving force of the universe to any one force cannot explain where the force that caused this force came from. For example, some people say that the first driving force is the movement of the earth's crust or the Big Bang. Then according to the law of conservation of energy, where does the force that causes the movement of the Earth's crust or the Big Bang come from? This is an endless process of tracing upwards. Attributing this power to God can resolve this crisis very well, because God is their belief, and belief is the unconditional belief in the existence of something supernatural, which does not need to be proven and cannot be proven.
Is something that cannot be proven still valuable? have. For example, the geometry we learn from childhood begins with an axiom, that is, a straight line forms between two points. What are axioms? The book says that this is knowledge that people have summarized from long-term life practice and does not need to be proven. In fact, the knowledge summarized in practice is not necessarily reliable. An axiom is a presupposition, which not only does not need to be proved, but also cannot be proved (it is not stated in middle school books and cannot be explained clearly). For geometry to continue to exist, these axioms must be believed unconditionally. Because of this, every once in a while an axiom appears in a geometry book, because without them geometry cannot continue. So what if these axioms are wrong? It doesn't matter, you really have to prove that the axiom is wrong and correct it, and this is how science develops. Moreover, according to Popper's theory, knowledge that cannot be falsified is not science at all!
The cleverness of Newton and others is that they already knew that there is no answer to this question at all. They might as well attribute it to God and become another belief in the minds of Westerners.