But how could we know if God exists? If He is outside of the universe, and outside of space and time, how could we point to Him? Is there any way to know, for sure, that there is a God?
Let's start with one of the most famous stories in the Bible - the giving of the Ten Commandments. As it turns out, this is a very very special event... perhaps the most important in all of history!
Most religions have a single creator, usually a gifted individual who has a divine revelation (Buddhism, Sikhism) or is visited by an angel in private (Islam). This makes them difficult to trust, especially because the people involved are imperfect.
However, out of all the religions in the world, only one is based on the testimony of an entire nation of people, whose ancestors entered into a covenant with the Creator over three thousand years ago. That religion is Judaism, and specifically the Orthodox branch of Judaism - the original and most observant of details.
Essentially, the Jews are claiming that they were chosen by the Creator of the Universe, blessed be He, to fulfill some special tasks and be a "light unto the nations", which is awfully convenient for them (aside from like, the Holocaust). We can trust in this collective testimony many millions of Jews have died rather than renounce their faith, which means that they are very serious about this and have been for thousands of years.
A central element of the Jewish faith - and therefore Christianity and Islam as well - is that the entire Jewish nation encountered God at Mount Sinai and elected Moses to receive the Torah on their - and our - behalf. Ever since then, the entire Jewish nation throughout history, and the Orthodox Jews today, maintain the memory of Sinai, the Torah they received there, and a wealth of other knowledge.
The key to understanding Judaism – or one of the keys – lies in a phrase you will hear from many religious Jews if you ask them about the source of their knowledge. That phrase is “I learned it from my rebbe”.
Far from being a philosophical “proof” of God written by a troubled European scholar, God's specific, timely, and intentional intervention in the affairs of the material world at Mount Sinai provides humanity with a verifiable memory of God’s existence and identity, supplemented by the written Torah. This is one of the main reasons why Jews are called by God to be a “light to the nations”, as in Isaiah 49:6.
Since the national revelation at Mount Sinai, the collective and internally-verifiable memory of this incredible event has been passed from Jewish parent to Jewish child in an unbroken chain, and also from teacher to teacher. Indeed, the system of education, ordination, and Biblical commentary employed by Orthodox rabbis is extraordinarily rigorous and stringent, which has helped to ensure the reliability of the information transferred over the centuries.