First, we can know Him through His Creation: ourselves, nature, and all of creation. All of this we can observe. Apostle Paul tells us, “For since the creation of the world, His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead” (Rom. 1:20). We can observe his wonders in the beauty of a flower, the flight of a bird, the snow caps of vast mountains or the beauty of a bubbling brook. We can see his vastness by the mystery of life of all forms, especially our own, and all its dimensions physical, mental, social, and spiritual. We can find it in the wonder and joy of the birth of a new child or the tender love a mother has for her newborn child.
Second, God revealed Himself to us through the Incarnation of the Son of God. God sent to us His only begotten Son who lived in the flesh. This is what is recorded in the New Testament. He also spoke to us through the prophets of the Old Testament. But, the incarnation of God himself as fully human gives us a most vivid way of knowing God. The Apostles are our best sources for information on this. Paul writes, “God, who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son” (Heb. 1:1-2). And John says, “And we know that the Son of God has come and has given us an understanding, that we may know Him who is true” (1John 5:20). So, one of the reasons God sent His Son to us was so we could know more about the nature of God.
So the answer to the question, “Where do we get the knowledge about God?”, is through our observation of Creation, the Scriptures and especially the life of the Son of God, Jesus Christ.
Beware of self-delusion
Knowing God is something that we cannot do on our own, because our minds are clouded by all the activities and assumptions of our current culture that basically denies God. We can easily make up theories based on assumptions buried deep in our subconscious mind. We must be aware that our mind can easily deceive us and even lead us into believing that there is no God. We need to be very careful. This does not mean that we don’t use our minds to know God, but we must have caution and seek proper guidance. To know God as best we can, we need to follow the guidance of those who have purified their minds through an exemplary Christian life allowing themselves to become capable of contemplating the exalted truths. In the Book of Matthew Jesus tells us, Blessed are the pure in heart; for they shall see God. (Matt. 5:8) Such people are often referred to as holy persons. Our Holy Church Fathers were supreme examples of such a person. Most commonly, our parish Priest is a good one to start with to help us along the path to knowing God. Alternately, a monk at a local monastery can also be helpful to us.