There is a popular story about how we can't fully understand God the Most Holy Trinity. But it doesn't mean that we can't have a relationship with God.

St. Augustine, who was instrumental in our faith, a bishop of North Africa in 4^th century, who was walking by the seashore one day. He was attempting to conceive of an intelligible explanation for the mystery of the Trinity. As he walked along, he saw a small boy on the beach, pouring seawater from a shell into a small hole in the sand. “What are you doing, my child?” Asked St. Augustine. The boy responded: “I'm trying to empty the ocean into this hole.” St. Augustine said: “But that is impossible.” The boy stood up and looked straight into the eyes of St. Augustine, and replied: “What you are trying to do – comprehend the immensity of God with your small head – is even more impossible.” Then the boy vanished. The child was an angel sent by God to teach Augustine a valuable lesson. Later on, Augustine wrote: “You see the Trinity if you see love.” In other words, we can understand something of the Mystery of the Most Holy Trinity more readily with our hearts, than with our feeble minds. God cannot be grasp with the mind so much as with the heart.