The doctrine of the Trinity is a classic, ancient, and central piece of Christian theology. When the church fathers and councils honed this doctrine, they did so in the firm conviction that it was biblical. They believed that God had revealed himself as the Trinity in Scripture. In this lecture, Fred Sanders presents the biblical case for affirming that the one God is Father, Son, and Holy Spirit, showing the lines of biblical reasoning that developed into the traditional doctrine of the Trinity. Often the biblical evidence for Trinitarianism is presented bit by bit, from one verse to another. This lecture instead emphasizes the big picture, especially the way the Old and New Testaments work together to bring out the doctrine..