Origins
To resist is, at its core, to stand your ground. The word comes from Latin resistere — re- ('back, against') plus sistere ('to take a stand'). The image is physical and immediate: a person planting their feet against an oncoming force.
Latin sistere was itself built on stāre, 'to stand', from Proto-Indo-European *steh₂-. This root may be the most prolific in English. Station, statue, state, stable, establish, instant, constant, circumstance, and substance all trace back to the same concept of standing.
The -sist family alone tells a story. To assist is to stand beside someone. To consist is to stand together. To exist is to stand forth into being. To insist is to stand upon a point. To persist is to stand through difficulty. To desist is to stand away — to stop.
Later History
Resistance entered English shortly after resist, and quickly found use in physics, politics, and everyday life. An electrical resistor opposes the flow of current. Political resistance opposes the flow of power. Even resisting dessert is an act of standing firm against temptation.
The French Résistance of the Second World War gave the word its most powerful modern connotation — ordinary people who stood against occupation.