Rejection of particular frequency in a signal which contains many frequencies in its spectrum (fourier transform)
I find the way you are phrasing your question a little confused but I think I know what you are looking for. I'll try to answer.

A circuit only sees (instantaneously) voltages - well yes, but there are elements on the circuit that are time-dependent. If we are talking about an analogue circuit, this is L's and C's. These elements store energy in one form or other, and release it with a rate which is variable depending on component value.

So now we have a circuit that has some "memory" characteristics. It's instantaneous state is dependent on the sum of all previous states. 

There are a number of ways of analysing this mathematically, but eventually we find that with certain circuit configurations we can arrange that the circuit's response varies according to the frequency content (Fourier spectrum) of the input. (This is one form of analysis that works well for periodic signals - signals which are assumed to behave in the same way, over and over, through all of time. In practice of course, nothing does this, but, say, a 1MHz waveform running for a second or two is close enough for the assumption to hold.)

Likewise a digital filter works by computing the instantaneous output based on some conmbination of previous (sampled) inputs. Now the memory element is really memory, used to store some number of samples in a rolling buffer.

In the end the important fact is that circuit behaviour has a time (and therefor frequency) dependent element.