Hebrews 1:1-4 nasb
“God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, 2in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world. 3And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power. When He had made purification of sins, He sat down at the right hand of the Majesty on high; 4having become as much better than the angels, as He has inherited a more excellent name than they.”
This Scripture shows that God has revealed Himself to man in 3 ways:
1. God Revealed Himself through the writings of the prophets, that is The Bible
Hebrews 1:1
“God, after He spoke long ago to the fathers in the prophets in many portions and in many ways…”
One amazing confirmation of God is the fulfillment of Biblical prophecy. Here are just a few of them.
Genesis 12:3 He (Jesus, the Messiah) would be of the tribe of Judah.
2 Samuel 7:12 He would be of the line of King David.
Micah 5:2 He would be born in the city of Bethlehem.
Isaiah 53 He would die with thieves and be buried in a richman's tomb.
Psalm 22:16, Daniel 9, Isaiah 49 and many others foretell of events that is impossible to fabricate.
2. God Revealed Himself through the birth, life, death and resurrection of Jesus Christ.
Hebrews 1:2
“God…in these last days has spoken to us in His Son, whom He appointed heir of all things…”
Jesus was not just a ‘good teacher.’ 
Regarding Jesus, the Son of God, Patrick Zukeran of Probe Ministries said:
He is either a “Liar, Lunatic, or Lord”
“A serious study of the Gospels leads a person to one of three conclusions about Jesus: He was (1) an evil lying villain, (2) a preposterously deluded madman, or (3) the Messiah, the Son of God. It is ludicrous for anyone who has studied His life to take the position that He was simply a good teacher. Only one of the three conclusions is a logical possibility”
Jesus told Philip that he was looking at God. Imagine, Philip was talking to God, Himself!
John 14:8-9
Philip said to Him, "Lord, show us the Father, and it is enough for us." 9Jesus said to him, "Have I been so long with you, and yet you have not come to know Me, Philip? He who has seen Me has seen the Father; how do you say, 'Show us the Father'?
Jesus told the Jews that He was alive even before Abraham was born. The Jews had no doubt regarding His statement, so they picked up stones to put Him to death.
John 8:56-58
"Your father Abraham rejoiced to see My day, and he saw it and was glad." 57The Jews therefore said to Him, "You are not yet fifty years old, and have You seen Abraham?" 58Jesus said to them, "Truly, truly, I say to you, before Abraham was born, I am."
Again in John 10:30-33
Jesus said,
"I and the Father are one."
31The Jews took up stones again to stone Him. 32Jesus answered them, "I showed you many good works from the Father; for which of them are you stoning Me?" 33The Jews answered Him, "For a good work we do not stone You, but for blasphemy; and because You, being a man, make Yourself out to be God."
1 Cor. 15:4-6
4and that He was buried, and that He was raised on the third day according to the Scriptures, 5and that He appeared to Cephas, then to the twelve. 6After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep;
3. God Revealed Himself through the Creation.
Hebrews 1:2-3
…through whom also He made the world. 3And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power. When He had made purification of sins, He sat down at the right hand of the Majesty on high;
Psalm 19:1-6 nas
The heavens are telling of the glory of God; And their expanse is declaring the work of His hands.
2Day to day pours forth speech, And night to night reveals knowledge.
3There is no speech, nor are there words; Their voice is not heard.
4Their line has gone out through all the earth, And their utterances to the end of the world.
In them He has placed a tent for the sun, 5Which is as a bridegroom coming out of his chamber;
It rejoices as a strong man to run his course. 6Its rising is from one end of the heavens,
And its circuit to the other end of them; And there is nothing hidden from its heat.
Another one is found in…
Romans 1:20-22
20For 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. 21For even though they knew God, they did not honor Him as God, or give thanks; but they became futile in their speculations, and their foolish heart was darkened. 22Professing to be wise, they became fools,
That’s it!! The Bible says God revealed Himself to man in three different ways. 1. By what He told the Prophets. 2. By being born of a virgin as the Son of God, His death and resurrection, and 3. by His wondrous works of creation.
Is this circular reasoning? Yes. Is it possible to prove God by extra Biblical evidence? No, not really. Rather it’s the extra Biblical evidence that confirms the Believer’s faith in the reality of God. The atheist or non-believer cannot be convinced. He ignores the wonders of God around Him. In any debate regarding God or not, there is always a basic pre-supposition. Disallowing the reality of God does not make it true. To the Believer, God is evident and self-explanatory.
1 Cor. 1:20
Where is the wise man? Where is the scribe? Where is the debater of this age? Has not God made foolish the wisdom of the world?
Psalm 14:1
The fool has said in his heart, "There is no God."
