8. How does God reveal himself in the Old Testament?

God shows himself in the Old Testament as God, who created the world out of love and remains faithful to men even when they have fallen away from him into sin. 

God makes it possible to experience him in history: With Noah he establishes a covenant to save all living things. He calls Abraham so as to make him “the father of a multitude of nations” (Gen 17:5b) and to bless “all the families of the earth” in him (Gen 12:3b). The people Israel, sprung from Abraham, becomes his special possession. To Moses he introduces himself by name. His mysterious name YHWH, usually transcribed Yahweh, means “I AM WHO I AM” (Ex 3:14). He frees Israel from slavery in Egypt, establishes a covenant with them on Sinai, and through Moses gives them the Law. Again and again, God sends prophets to his people to call them to conversion and to the renewal of the covenant. The prophets proclaim that God will establish a new and everlasting covenant, which will bring about a radical renewal and definitive redemption. This covenant will be open to all human beings.

7. Why did God have to show himself in order for us to be able to know what he is like?

Man can know by reason that God exists, but not what God is really like. Yet because God would very much like to be known, he has revealed himself.

God did not have to reveal himself to us. But he did it — out of love. Just as in human love one can know something about the beloved person only if he opens his heart to us, so too we know something about God’s inmost thoughts only because the eternal and mysterious God has opened himself to us out of love. From creation on, through the patriarchs and the prophets down to the definitive revelation in his Son Jesus Christ, God has spoken again and again to mankind. In him he has poured out his heart to us and made his inmost being visible for us.

6. Can we grasp God at all in concepts? Is it possible to speak about him meaningfully?

Although we men are limited and the infinite greatness of God never fits into finite human concepts, we can nevertheless speak rightly about God. 

In order to express something about God, we use imperfect images and limited notions. And so everything we say about God is subject to the reservation that our language is not equal to God’s greatness. Therefore we must constantly purify and improve our speech about God.

Vittore Carpaccio (1460 - 1525/1526): St. Stephen Preaching

So it happens that men in such matters easily persuade themselves that what they would not like to be true is false or at least doubtful.

Pope Pius XII

They [men] should seek God, in the hope that they might feel after him and find him. Yet he is not far from each one of us, for “In him we live and move and have our being”.

Acts: 17:27-28a

4. Can we know the existence of God by our reason?

Yes. Human reason can know God with certainty. 

The world cannot have its origin and its destination within itself. In everything that exists, there is more than we see. The order, the beauty, and the development of the world point beyond themselves toward God. Every man is receptive to what is true, good, and beautiful. He hears within himself the voice of conscience, which urges him to what is good and warns him against what is evil. Anyone who follows this path reasonably finds God.