God knows everything, including the future.
GOD existed before everything else, which He Himself created.
Humans mark time based on the solar system (earth's revolutions, position to the sun, phases of the moon, etc.). GOD existed before the solar system, which He created. Therefore, GOD exists outside the confines of human time.
The Bible asserts that GOD knows everything, including:
- That which is seen and unseen by human eyes
- That which existed before, exists today and will exist in the future
- Individual spirits and souls which He creates and forms within the mother's womb
- The thoughts and intentions of our hearts
- The words we speak, even before we speak them
- The actions we take, even before we take them
- The impact of future events
- Perfect recollection of every past event (mental or actual)
- What happens to us, individually, after we die and leave this life, even before we are born
Regarding these things, King David wrote:
1 ... O Lord, You test me and know me;
2 You know my sitting down and my rising up;
You understand my thoughts from afar;
3 You search out my path and my portion,
And You foresee all my ways.
4 For there is not a word on my tongue,
5 But behold, O Lord, You know it altogether,
The last things and the first things;
You fashioned me, and placed Your hands on me.
11 And I said, “Perhaps darkness shall cover me,”
But the night shall be light to my delight;
12 For darkness shall not be dark because of You,
And the night shall be bright as day;
As its darkness, so also shall be its light.
13 For You possess my heart, O Lord;
You took hold of me from my mother's womb.
14 I will give thanks to You,
For I am fearfully and wondrously made;
Marvelous are Your works,
And my soul knows this very well.
15 My bone you made in secret was not hidden from You.
And m substance was in the lowest parts of the earth;
16 Your eyes saw me when I was unformed,
And all men shall be written in Your book;
They shall be formed day by day,
When as yet there were none among them.
(Psalm 138 :1b-5, 11-16 OSB)
Likewise, when GOD called the prophet Jeremiah, He said:
4 Thus the word of the Lord came to me, saying, 5 “Before I formed you in the womb, I knew you, and before you were born, I sanctified you. I established you a prophet to the nations.”
(Jer. 1:4-5 OSB)
The Bible is full, from cover to cover, of the records of GOD's promises and prophecies regarding future events that came true just as He said. The evidence, both within the Scriptures, as well as external sources which testify to their accuracy, including from sources who were enemies of the Jewish and Christian faith, is one of the biggest reasons why so many people believe and have believed that the Bible is divinely inspired and that the GOD of the Bible really exists.
If you would like to research evidence regarding Scripture's accuracy, I recommend Josh McDowell's book, The New Evidence That Demands a Verdict.