Some things can be known about God by observing the creation, but other things can only be known by revelation (the Trinity for example). The use of Aristotle in theology and philosophy was controversial in the 13th century. Instead of Plato’s ideas of concepts innately understood – already hard-wired into our brains as it were, Aristotle emphasised what could be observed by our senses. Nevertheless, while Thomas agreed with the value of human reason, he also emphasised the role of scriptures in revealing God and the role of the church in protecting theology from heresy.
Thomas wrote a great deal about God and how he can be understood. Especially about how we can speak about God. What do we mean when we say God is loving or good? He used the concept of analogy. We understand in a small way something about God as loving by analogy to what we know of human love. So what we say about God is like what we mean when we talk about humans but not quite the same.
The nineteenth century saw a huge growth in the influence of Thomas as the great explainer of Roman Catholic doctrine. However his influence for protestants has been overshadowed by the work of the reformed theologians who tended to use Augustine as their teacher.
Dale