> What must the Aztecs thought of the Spaniards whose holiest emblem is a man being publicly tortured to death.

The meaning and symbolism would have been blindingly obvious to them. In general, Christian and pagan theology is basically the same. Christianity is a direct development of pagan thought.

The modern thought framework for 99.9% of modern people is Gnostic, not Christian. Both Christianity and paganism is thus completely impenetrable and incomprehensible for pretty much every person alive today.