Theology is doubly revealed and many Christians often ignore God’s natural revelation as being a valid object of interpretation. It’s all too often that many Christians reject many valid scientific theories.
“Theology is properly distinguished as natural and revealed. The former is concerned with the facts of nature so far as they reveal God and our relation to him, and the latter with the facts of Scripture.” –Charles Hodge
Theology refers to the all encompassing knowledge of God.
Theology of Nature refers to the Book of Nature as revealed in Scripture (Ps. 19.1-4; Rom. 1.20) Look at Psalm 19. When speaking of God it refers to his general name (El, Heb., continuous, abundant, universal). Some of the themes are creation’s contingency, Imago Dei, Stewardship, the fall, etc.