Both Panasonic GX7 and Fujifilm X-E2 have 16.0 MP resolution sensors but Panasonic GX7's sensor is Four Thirds (17.3 x 13 mm ) and Fujifilm X-E2's sensor is APS-C (23.6 x 15.6 mm ).
Since Fujifilm X-E2's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Panasonic GX7.
Below you can see the GX7 and X-E2 sensor size comparison.
As seen above, Fujifilm X-E2 has a 1.6x Larger sensor area than Panasonic GX7. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.