The Bible teaches that God is a Trinity. There is one God in three persons. All three persons share the same essence / substance, yet they are distinct persons with unique roles.
How would you show someone from the Bible that the Holy Spirit is God, and He’s not just some Christian equivalent of a mystic force? There are at least two ways you could talk about this from the pages of the Bible:
The Holy Spirit has all the same attributes as God
-Eternal - Hebrews 9:14
-Power - Luke 1:35
-Omniscience - 1 Cor 2:10-11
-Creator - Gen 1:2; Ps 104:30
The Holy Spirit is used interchangeably with God the Father and God the Son
-Acts 5:3-4
-Rom 8:9-11
-Matt 28:18-20
You could also use the logic in these same verses to understand that the Holy Spirit is a person and not just a spiritual force.
One of the reasons this doctrine of the Holy Spirit is so important is because the Bible teaches that God has given His Holy Spirit to every believer. The fact that He is a person means that we have a relationship with Him. We can grieve Him, He can help and counsel us - all of these aspects of the Spirit’s ministry are because He is a person and not just a superpower that God gives us when we are saved.
The Spirit dwells in us (Eph 1:13-14; Rom 8:9-11). That means that God dwells in us. That is part of the good news of Christianity. Not only have we been declared righteous by the judge of the universe, but He has come to dwell in us. He doesn’t just forgive us and then hope that we’ll have enough gratitude and motivation to follow Him. No, He guarantees that we will grow and follow Him by dwelling in us and working inside of us.
The reason we’ve grown to where we’re at is because God has brought us here. The reason we will not stay here, but will continue on in holiness is because God is in us and will continue to sanctify us.