When we speak of potential difference between "two points"- we speak of voltage - for example in a battery the difference of electrons between the negative and positive terminal is voltage, In other words, negative terminal has excess of electrons and positive has deficit of electrons and the difference between the two is voltage. So when electrons flow through the resistor once the battery is connected to a circuit, we measure the potential difference across this resistor and "confirm" that voltage has dropped (through voltmeter) but the rate of flow of current before the resistor and the after the resistor is the same (in a series circuit at least). In other words, there is no difference in electrons - so there is zero potential difference between these two points, hence there is no voltage. So what does this mean? Sorry if this is a dumb question.