Without the Holy Spirit, Christian discipleship would be inconceivable, even impossible. There can be no life without the life-giver, no understanding without the Spirit of Truth, no fellowship without the unity of the Spirit, no Christlikeness of character apart from his fruit, and no effective witness without his power. As a body without breath is a corpse, so the church without the Spirit is dead. Luke is well aware of this and emphasizes the power of the Spirit throughout Acts, especially in Acts 2, which is all about the day of Pentecost, when the Spirit comes.