If I take a point source and place it in space it would emit light spherically in all directions around it. You will be able to see a point, only if the rays from that point reach your eyes. This means that you will be able to see a point source from any place around it. If u just had a sensor (retina) and not the lens in your eye, these rays that are diverging and almost everywhere in space would fall all over the retina to form an image which would be a uniform light patch in your brain. The same applies to non light sources as well. You will be able to see an object only if the object is reflecting light in the direction you are seeing. Again an object can reflect light in almost any direction around it. Without the lens, the reflected light from many points around you can fall at the same place on the retina as shown below.
The intensity and frequency of the reflected light from these various points can be different and hence get summed up at a point on the retina. This scenario can happen for every pixel on the sensor and hence the image that you will get will just be the summation of the intensities and frequencies of the rays coming out from various points around you. As a result of this you will always end up with a uniform patch of light on the sensor if you try to take an image without a lens.
If you didn’t have a lens in your eyes, you would only be able to know the amount of light present in the surrounding and not the objects present in front of you. The various objects wouldn’t be distinguishable at all.
To see a point as a point, we need to converge the rays that are diverging from it, to a point again. The lens does exactly this. Your brain sees various objects around it as they are because your eye lens converge the rays coming from it on the retina.
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