If you ever ride a bicycle – you know how amazing that a bicycle with gear allow you to “match” your muscle (energy source) to any landscape (load). Essentially the gear match the source to load just like the way transformer match an AC source to its load.
Let’s look at a simplified diagram of the torque that your leg muscle generate versus the landscape – slope degree.
Assuming that at gear ratio of 1:1, for every turn of pedals the wheel will turn by one cycle, then:
Low Gear (1:0.5) means for every turns you make on the pedals, the wheel only make half a turn, since your leg muscle power is constant, your loss on speed is made up with your increase of forward force.
High Gear (1:2) means for every turns you make on the pedals, the wheel only make 2 turns, since your leg muscle power is constant your gain on speed is made up with your reduction of forward force.
Now compare this to the impedance matching in audio amplifier:
Picture from Wikipedia - transformer to perform impedance matching