The Apostles’ Creed states: “I believe in the Holy Spirit.” Who is the Holy Spirit and what does he do?

Both the Spirit and the Son are called intercessors—they are nonexpendable in the work of our intercession (or prayer). And this by necessity requires the Father, too. How does knowledge of the Trinity strengthen our prayer life?

Many Christians struggle with how to give a sound definition of the Trinity. Why does the doctrine of the Trinity matter for every believer?