"The secret things belong to the LORD our God, but the things revealed belong to us and to our children forever, that we may follow all the words of this law."
Our very knowledge of God is bounded by only the extent to which he has revealed himself to us. There are many great mysteries far too great for above our comprehension. What he has revealed is all we needed to know for our salvation and benefit. More importantly, God's truth as it is revealed through God's Word (both the Incarnate Christ and the Scriptures) belongs to us and our children.
God in the fullness of his revelation is a God for us purposed in Jesus Christ. Theology, therefore, is just a restatement of what God has already said of himself. We know nothing unless God reveals it, for the secret things are his. Theology is synonymous with "Christianity" because Christ is the image of the invisible God and the fullness of God in Man. So every Christian is a theologian for Christ is revealed to each one.
Truly, because of the illumination of the Holy Spirit, we can know God in the same way God knows himself, if only in miniature. And yet, even with all this revelation, it is but the tip of an infinite God for we still say with all sincerity, "Oh, the depth of the riches of the wisdom and knowledge of God! How unsearchable his judgments and his paths beyond tracing out!" (Rom 11:33)