Peter Kreeft has an interesting way of explaining how we see with the eyes of faith. He refers to seeing with our "first" eye as using our bodily senses (sight, hearing, touch, smell and taste), seeing with our "second" eye as using our mind or our reason, and seeing with our "third" eye as using our heart.
Anyone, animals included, use the first and the second eyes to see with. The first is simple data gathering. There is a wall there. There is light coming in through the cracks in the wall. The second eye reasons. The wall is old and must be broken to be letting in the light. The third eye however is used only by humans. We go beyond reason just as reason goes beyond data gathering. The third eye will look at the same crack in the wall and see along it. It will see the hole reveals a world outside. That the light is coming from the sun (which cannot be seen directly via the crack) and that it indicates a way out of the room. There is more here than what meets the eye.
This third eye is how the heart sees. It is also referred to as seeing by faith. Animals do not understand a book, for example. The dog sees the page. It sees the markings on the page. However it does not understand that the markings point beyond themselves to concepts beyond the print. Only human beings can make the leap from a thing to what that thing symbolizes, to what it points to.
To a materialist, science is the limit of what can be seen. The second eye, while very powerful for understanding and connecting the physical universe, is not sufficient to understand what cannot be seen by it. To a materialist, a marriage is a simple pair bonding wholly explained by physical interactions, hormones and mutual advantage. There is no more because the second eye can see no more. On the other hand, the third eye can see that a marriage points to something beyond itself. It is a sign of the love of God in the Trinity. It understands that a man and a woman are created to be united as one in marriage, expressed in part by the physical, but the ultimate meaning of the marriage dwarfs the mere physical.
Just as reason makes sense of the data, the heart makes sense of reason. This is not to say the heart is irrational, but that it goes beyond the merely rational. As Pascal puts it, "The heart has its reasons of which reason knows nothing."