Unbelievers find the Christian doctrine of the Trinity confusing and contradictory, and believers sometimes are confused about what the point of the Trinity is. But the Bible insists the only way to really know God is to know him in the story of the Bible – a story that describes him, even as early as Genesis 1, as existing in multiple persons and then, later, as One.
This notion of God as always existing in a relationship of three people is key to knowing who God is. He is not primarily a God of power, and even not primarily a God of holiness, but a God who primarily is love.
In this sense, the heart of a belief in God is a belief in the eternal, perfect, infinite love which God has for us as our Father, united to our brother Jesus, and connected to this relationship by the Holy Spirit.