Both Fujifilm X-A5 and Sony A7 have 24.0 MP resolution sensors but Fujifilm X-A5's sensor is APS-C (23.5 x 15.7 mm ) and Sony A7's sensor is Full frame (35.8 x 23.9 mm ).
Since Sony A7'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 Fujifilm X-A5.
Below you can see the X-A5 and A7 sensor size comparison.
As seen above, Sony A7 has a 2.3x Larger sensor area than Fujifilm X-A5. 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.