A big difference between 4d space and spacetime is its size. Consider the size (Cardinality) of all the sets which have a one to one mapping between the digits on my hand and their members to be 5. Define the Cardinality of the set of all integers as $\aleph_0$, said as aleph-null. Note that it is possible to produce a 1 to 1 mapping between the set of integers and the set of even integers. This is a property of infinite sets, they have 1 to 1 relationships with proper subsets of themselves, and these subsets have the same cardinality as the original set.
Note that $\aleph_0+\aleph_0=\aleph_0$. The set of Real numbers is composed of Integers + Fractions + Irrational + Transcendental numbers. The cardinality of Integers Fractions and Irrational numbers is $\aleph_0$. The cardinality of transendental numbers is $\aleph$ which is larger than $\aleph_0$ (probably $\aleph_1$ but not proven to be). $\aleph_0+\aleph_0+\aleph_0+C=C$ and this is the cardinality of the points on a line. A line is a proper subset of 2d space so the cardinality of 2d (and by extension any_d) space is C.
Spacetime may be imagined as your monitor consisting of C pixels each of which may represent any colour. Replacing the monitor with 3d space and the colour with time infers that spacetime has C points. This is F (probably $\aleph_2$ again not proven) because it is also the cardinality of the set of all single valued functions.
We have N < C < F. This makes it possible to resolve Zeno's paradoxes by having the arrow stationary in spacetime but moving in 3d.
This is called Relativity and would be the mathematical framework for a 3d universe moving through some other thing. Special Relativity and General Relativity continue the Relativity tag because it was thought that the universe would be explained based on this model. It turned out that realizing that the arrow and the observer have a different understanding of what is NOW is more fruitful.