In Millard J. Erickson's book Christian Theology: 3rd Edition, he sets out to explain several Key doctrines of the Christian faith. Concerning the doctrine of God, he separates his thoughts into four parts. I will use three as an outline for writing this summary. The parts are as follows: 1. Studying God. 2. Knowing God. And 3. What God does.
1. Studying God
To study God, we must understand two forms of revelation. General revelation and specific revelation. We will start with specific revelation, such as the scriptures, which point us to general revelation and what it intends to say.
In the scriptures, the existence of God is assumed by each writer. From Genesis 1:1 "In the beginning God," to Exodus 3:14, "I AM that I AM," along with countless New Testament references, God's aseity is assumed. Special revelation does not make an argument for God's existence as it expects the belief that He does. However, special revelation does point to general revelation as evidence for God's existence. For example, Romans 1:20 says,
"For since the creation of the world His invisible attributes, His eternal power, and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse."
Notice that the context of Romans 1 is not an argument against unbelief but rather an argument for God's righteousness. Even those who disobey in Romans 1 don't necessarily deny God's existence.
2. Knowing God
Knowing God requires a study of His attributes, which we also derive from both special and general revelation. Included among these attributes are things like: God is Spirit (John 4:24), God is love (1 John 4:8), God is omniscient (1 John 3:20, Isaiah 46:9-10), God as omnipotent (Job 42:2, Psalm 33:6), God's omnipresence (Isaiah 57:15), and God's eternality (Romans 1:20). We, of course, go on from this to the moral attributes of God in things like Holiness, righteousness, and mercy.
Knowing about God is one aspect of the doctrine of God, but knowing Him in a personal way is also vital. The scripture communicates a God who longs to dwell with His creation. We need only look to the bookends of the Bible, Genesis, and Revelation, to see the way the story began is precisely how the story will end as God brings about the restoration of all things.
3. What God Does
What God does is contingent upon who He is and of course that He is self-existent. That is to say that if God is righteous, then He necessarily judges righteously. If God is merciful, then He necessarily loves mercy. If God is Holy, then He is altogether set apart.
Mere principles of God's character are one thing, how they play out in creation reveal to us a more expansive meaning. For example, the scripture tells us that God is love. The actions of God include that He lays down His life for His creation. Therefore, our understanding of love Goes far beyond what we assume in human terms. In a manner of speaking, what God does is shaped by what the scriptures say of Him.