As Christians, we believe in one God, with three distinct identities: Father, Son, and Holy Spirit. The first two of these, are pretty easy to understand, at a basic level. God the Father is the big guy in the sky, God the Son is Jesus, God in human form, but the Holy Spirit? That's tougher to wrap our tiny human brains around. This series looks at what Jesus said about the one who would come after him, the holy spirit.