I’ve noticed that discussions on the Trinity between Muslims and Christians tend to focus on God and Jesus. But it makes no sense to talk of “Trinity” without also focusing on the third person: the Holy Spirit.
In the book of Acts there is an incident where Peter, one of the apostles of Jesus, equates lying to the Holy Spirit with lying to God. Peter says, “Ananias, how is it that Satan has so filled your heart that you have lied to the Holy Spirit and have kept for yourself some of the money you received for the land? Didn’t it belong to you before it was sold? And after it was sold, wasn’t the money at your disposal? What made you think of doing such a thing? You have not lied just to human beings but to God.”
Elsewhere in scripture it’s made clear that the Holy Spirit can be grieved and blasphemed against. It’s for this and many other reasons that Christians affirm the Holy Spirit is personal and relational, not merely an impersonal force or an emanation of the power of God. We believe that through the Holy Spirit, God guides us, empowers us, and sanctifies us. No discussion of the Trinity could be complete without the Holy Spirit of God and Jesus.