One of the serious problems with classical physics is the presumed possibility of action at a distance. Mathematically, it is possible to treat the net force on a particle as if it is the result of a "field" where the field strength at any point in space is the vector sum of all the individal sources of force.
For example, the electric field in a space containing four protons can be calculated at any point in space by assuming that a sample charge exists at that point and is being acted upon by the four protons. Once you know the value of the field, you can ignore the protons.
The problem with this is that the field then becomes the cause of motion of a particle being acted upon. There is no delay associated with the distances to the protons. If one of the protons moves, the field would instantly reflect that motion and any sample charge would feel this effect immediately.
In the real universe, there is a delay between the motion of a charged particle and the effect on another particle at a distance. For electric charges in free space, that delay is dictated by the speed of electromagnetic radiation; photons.
The analogy I think of for exchanging particles, is that of two platforms sitting ten feet apart on a frozen lake. Imagine a man standing on each platform and taking turns throwing a ball back and forth. When the man on the right throws to the left, he imparts leftward momentum to the ball and a equal rightward momentum to the righthand platform.
When the man on the left catches the ball, the ball transfers its leftward momentum to the platform on the left. When the man on the left throws, he transfers rightward momentum to the ball and leftward to his platform.
The result is that the platforms drift apart as if a force were causing them to be repelled. If something should cause a shift in the position of one of the platforms, the effect of that shift could not be detected until sufficient time had passed for a ball to travel between the platforms.