In the beginning was the Word,
and the Word was with God,
and the Word was God.
He was in the beginning with God.
All things came to be through him,
and without him nothing came to be.
What came to be through him was life,
and this life was the light of the human race;
the light shines in the darkness,
and the darkness has not overcome it.
John 1:1-5
Theology is, quite simply, "the study of God". Theology strives to answer not only "Who" is God, but also "Why" is God? Why does God do what He does? Why did He make you or me or the universe to begin with? Did He need to? How do I enter into a deeper union with the Creator through prayer and contemplation?
The Great Thinkers who came before Christ was incarnate -- Plato, Aristotle, and others -- were already laying the groundwork for great minds like Saint Augustine and St. Thomas Aquinas, who recognized a godly inspiration in their predecessors' philosophy on human existence, even if they were only scratching the surface. The Catholic Church produced -- and continues to produce -- intellectual giants who never stop asking the question, Who is God? In short, we will never know Him entirely -- not even in Heaven -- because there is no end to Him; He is eternal. But what He *has* transmitted to the Church throught Divine Revelation, and the great Doctors of the Church through Inspiration, can raise our faith to new levels of understanding, and keep us in sheer awe of our loving and merciful Father in Heaven.
If you've never read theology, the best advice is to take it slow and be prayerful. There's no rush. You have all eternity...