Purpose of a resistor in active filter circuit
This is a second order Sallen-Key filter.

R17 is basically a piece of wire, at least compared to the input resistance of the op-amp, and sets its gain to approximately unity.

Why use a resistor instead of a bit of wire? It's the same value as R18. This means that input bias currents drawn by the amplifier tend to create the same drop in R17 and R18, giving the filter as close to zero DC output as practical, for that class of op-amp. If you really want zero DC output, then there are opamps with better voltage offsets than the LF356. With its typically 30pA input bias current, the offset voltage in 22kohms is negligible.

Were it a much much faster opamp, then you would find it modifying its frequency response, especially if there was significant stray capacitance to ground at the inverting input.