You have attributes that both you and others recognize. Others might even characterize you by some seemingly dominant attribute, say your kindness, your generosity, your anxiety, your anger. Deep down they know, as you know, you aren’t an attribute, that you have more than one attribute, and that, even, for example, if you are continuously kind, you can also be envious or avaricious or slothful. You aren’t, you would say, simply your chief attribute because you don’t want to be labeled, defined, and pigeonholed as one attribute personified. Even though some attributes might be universally praiseworthy, the thought of being limited to a single attribute denies your true complexity.
So, God, as the argument goes, is different. Oh! Yes. There’s that obvious eternal omniscient and ubiquitous stuff that separates the Infinite from the finite, but there’s another difference between the Divine and you in the thinking of Aquinas and others. God IS His (Just get over choosing a gender in this) attributes. You might be merciful; God, in contrast, IS Mercy, or Justice, or Omniscience, or Omnipresence. Interestingly and somewhat ironically, the concept of divine simplicity allows for many attributes, posing a problem for our chatty neurons: How do we explain being many yet simultaneously being simple? (Don’t try to solve this problem today)
Ignore that the principle of divine simplicity might be a bit of a contradiction because of all those attributes, and focus on the idea of associating attributes with individuals of our own finite kind. We say, for example, that people with apparent motiveless malignity who walk into a church, temple, or mosque to shoot strangers are not just evil actors, but ARE EVIL. Our personification of such heinousness is understandable because some acts exceed our ability to understand fully the complexity of human thought and behavior. One of our attributes, rationality, has particular difficulty with such acts. We simplify our understanding by associating attribute and individual. In a sense, we apply a Thomist concept to a finite human.
Put heinous acts aside. Do we do the same with “ordinary” people? Do we ascribe a simplicity to those around us based on some attribute we designate as a chief character trait? Are we like those anonymous social media users who pigeonhole, define, and label? If so, are we not ascribing a simplicity that, in fact, can’t coexist with complexity in a finite human being? You and I HAVE multiple attributes, and so do all others, but we are not personifications of those attributes. If we were, wouldn’t we be Godlike? And isn’t it ironic that those who would conflate attribute and person for purposes of denigration are actually ascribing a divine simplicity to those they intend to defame?