Santayana in his autobiography refers to Catholicism as the most human of religions, if treated humanly. He does so because, he claims, it is fundamentally pagan (it has a pagan foundation), but supplements paganism with metaphysics. By "pagan" I think we must assume he means pagan, pre-Christian, religion as opposed to pagan philosophy. Much of pagan philosophy seethed with metaphysics, of course.
I'm interested in the "if treated humanly." I happen to think that metaphysics, though it clearly has occupied human thought (far too much), is not particularly human. This is because I think it to be concerned with matters that should not occupy humans to any great extent. It should not because, much as it may be pretended otherwise, it does not address human concerns. It seeks to transcend the miserably mundane world in which humans live, act, love, hate, procreate and die. If it could, it would ignore humans utterly, as well as the world in which they live. The truth as well as anything truly important to metaphysicians is to be sought elsewhere.
If I understand Santayana correctly, he may disagree with me about metaphysics. However, he also seems to feel that Catholicism, and by implication I think all religion, is treated humanly when it is treated as a human activity; in other words, as conduct on the part of human animals by which they seek to experience transcendence. Religion, therefore, is a very human, very natural, activity.
"Activity" is an important word here. Humans are inclined to action and inclined to act in a particular way when being religious. They have engaged in rituals while being religious for thousands of years. Particular actions have been deemed to allow us to partake of the divine in some special sense. Catholicism took on many ancient pagan rituals prevalent in the Roman Empire just as it took on much of the empire's administrative organization. Generally, rituals are presided over by a priesthood--those peculiarly knowledgeable regarding the ritual.
Catholicism as it was practiced in Santayana's time was still very much devoted to ritual. One could go to a Church anywhere in the world and observe the same ritual performed in the same Latin. The Reformation sought to do away with ritual, as well as a kind of priesthood, and the use of images (idols, icons) in the ritual. Catholicism sought to do the same with and after Vatican II.
Christ became in that way more human than divine. There is little or nothing new under the sun, it seems. In the ancient Church, there were many who refused to accept Christ as divine in the same sense as the Father. Using the metaphysics of the time, they thought him of similar substance to the Father, but not of the same substance. Eventually, this view was made a heresy, and the Church proclaimed Christ to be "one in being with the Father." Icons were also condemned by some in the ancient Church, and this to was eventually condemned by it, only to come up again in Protestantism, and now. We have a rather unfortunate way of repeating ourselves.
I suspect we will be tending towards ritual again in our religion, soon enough. We may have already commenced that movement. The spare, dull, communal "happy" get-togethers which were religious celebrations the last time I visited one seemed to me particularly bland.
I don't mean to claim that ritualistic religion is in some way better than other religion. But like Santayana I suspect that we humans find ritual to be comforting, and pleasing, even in a profound sense.