According to Jewish tradition, Abram arrived at the conclusion that there was only one true God worthy to be worshipped before God spoke to him or through the process of natural revelation. An interesting story is told in this regard. His father Torah was an idol maker and one day left Abram in charge of his showroom. Abram smashed all the idols except one in whose hand he placed the hammer. When his father returned he demanded to know what had happened. Abram told him that the idol with the hammer had broken all the other idols. Terah said, "Do you think you'll fool me? These idols do not know anything." Abram replied, "Do your ears not hear what you mouth has just said"? (David Klinghoffer, The Discovery of God, Doubleday, NY,2003,pp.20-21) In other words, how come you make and sell to the people gods who are not really gods?
In God's dealings with mankind his "speaking" is heard but how does the invisible God speak to man and how can man be reasonably sure it is really God speaking rather than delusion?
Abram was the first man in history who heard God speaking to him. Abraham c. 1,900 BC had migrated with his father Terah from Ur of the Chaldeans and settled in Haran. It was in Haran that Abram heard an inner voice prompting him to leave his father's house for an unknown land. So Abram began to move but had doubts when God promised land. "O Lord GOD," he asked, "How am I to know that I shall possess it?" ( Gn 15:8) So, God told him to cut some animals in half , symbolizing the two parties to the covenant, and in the night passed between them as a flaming torch
God also promised Abraham that he would be the father of a great nation. One day God appeared to Abraham as three "mysterious visitors" who revealed to him that Sarah would have a child in a year. Abraham laughed and thought to himself "Can a child be born to a man who is a hundred years old? Or can Sarah give birth at ninety?" (Gn 17:17) And so a year later Isaac was born. From this we can see that the faith Abraham placed in God was not an illusion but what God said he confirmed by signs.
Jacob, the son of Isaac, also experienced an encounter with God at Bethel while on a journey to Haran. During the night Jacob had a dream where God appeared to him. God identified himself as the God of Abraham and Isaac. He made to Jacob the same promise he had made to Abraham and protection on his journey. Jacob is unsure what to make of this dream and must have asked himself,. "Was it really God who spoke to me?" So Jacob vows that if God protects him on this journey and he returns safely home "the Lord shall be my God". (Gn 28:20)
The revelation of God to Moses came by the sight of a burning bush on Mt. Hobeb which was not burning. The fire was probably a projection of his own mind engendered by God to get his attention. As he drew closer he heard the voice of God speaking, interior or exterior or both, we do not know.
Once again God identifies himself as the God of Abraham, Isaac and Jacob and tells Moses to deliver his people from the slavery in Egypt. God offers Moses proof that it was the God of his fathers speaking to him, "when you bring my people out of Egypt, you will worship God on this holy mountain." (Ex 3:12) Moses was not satisfied and asks for a name that he could tell the Israelites in Egypt. God told him (Yahweh) meaning "I Am who I Am".
God here reveals his personal essence and identity and so we speak of the personal God. What does this mean? From the Christian perspective we know that God is Three Persons in One, that they live in one another and act in unison with the same purpose. To Moses, at this stage of revelation, God appears as a single entity speaking. God is personal because He began an I-Thou relationship with him. He is no longer the abstract God of the philosophers or the unknown God of the Eastern mystics, but a God who communicates by "words" and actions with his people. Moses still fears that the Hebrews in Egypt would not believe him, so God shows Moses that his staff could change into a snake and that his hand could become like that of a leper. Once again God backs up his presence by signs and wonders so that they may believe.
From the above we can see God's revelation to mankind is not unreasonable because God backs up his message by signs or events that can be verified and that this revelation is unique in the history of religions. He is God who reveals himself and hears the pleading of his people, "Rescue me from my enemies, my God; lift me out of the reach of my foes." All of the psalms brings us into a relationship with God which reveal the belief in a Personal God.
The Word as Tradition