Light speed is a finite quantity, so it takes time for light to travel cosmic distances. The "lookback time" of early galaxies tells us that the ones we can see are located very far away. This makes them difficult to observe because of their apparent size and brightness, and gravitationally lensed images of these faraway galaxies (specifically the magnified versions) can be better observed and studied since they are brighter than their un-lensed counterparts. I like to think of it as if we are putting those faraway galaxies under a microscope (of course, that's not what is actually happening, but the idea is similar).