Some people, Aquinas tells us, think that sacrifices and other signs of devotion to God can also be offered to any kind of superior being, even a superior man. But as Aquinas bluntly puts it, this line of thinking is irrational. While we should properly respect our superiors, a unique reverence is due to God, who excels all other beings. Christianity is not just concerned with external signs. It requires proper thought and action.
Words are audible signs.
When we say we worship God, we in fact worship Him. We deliberately distinguish our acts of worship from other acts. Many will suppose, Aquinas continues, that our sacrifices and prayers are little more than customary actions that are performed simply because our ancestors have followed them. In a time of persecution, it may be legitimate to worship idols exteriorly while interiorly withholding our assent. This argument, Aquinas maintains, is manifestly false.