Is it a scientific illusion or religious miracle?
Seeing things we cannot explain is not an uncommon occurrence for us. The cultural debate as to why we see the face of Jesus time and again on food is more than likely to go on for a long time. It can be zeroed down to these factors.
This may be the most scientific and the most logical reason as to why people see this face. It is an illusion that causes the human brain to see non-existent faces. It is caused by the interaction between the frontal and posterior visual cortex, where the previous controls or produces expectations of what a certain object is supposed to look like while the latter processes images for the brain. Tricks involving light also play a crucial role in face pareidolia. Bottom line, the mind plays tricks with the light and we are able to see images or figures that we want to see.
This is the most common reason yet. Human beings are wired to have something to explain things that cannot be understood. The religious beliefs of some people lead them to see faces in their food, particularly for Christians, the face appears as that of Jesus or The Virgin Mary since part of them needs something to hold on to and to prove that an unknown force is still actually watching over them.
For children who are brought up in front of television screens and cartoon characters, it is not uncommon for such children to have a very active imagination. Their indulgences burn a certain perception of reality into them. Such children are able to distend characters from their minds. If they are exposed to enough religious programs, their minds will most definitely project their imagination outwards and they will see the face of Jesus at one point or another in their lives.
Each human being may have a different or more specific as to why they view Jesus on their food, but basically, all the reasons are narrowed down to these macro classes.