In Act 8:15-17, what is the Holy spirit concretely? According to the Bible, God is spirit.
In Act 8, many people want to receive the Holy spirit. I want to know what is the Holy spirit
and I want to know why many want to receive it, even Simon at that time.
What is the Holy Spirit?
According to the disciples - from whom came some of the Apostles, they understood the Holy Spirit to be the spirit of the Father - the "only true God", as Jesus explained, who had sent him into the world.
for the Holy Spirit will teach you in that very hour what you ought to say." Luke 12:12
for it will not be you speaking, but the spirit of your Father speaking through you. Matthew 10:20
So, the Holy Spirit and the spirit of God are exactly the same.
The Church founding fathers, the Apostles, Paul, Peter, Timothy etc did not believe the Holy Spirit to be a person or part of a tri-part God. This new idea came 100's of years after these men Jesus had appointed to lead the new church.
We see in Acts 8:20
But Peter said to him, “Your silver, may it perish with you, because you thought the gift of God to be obtained by money!"
Peter called this spirit a gift from God. It is the presence of God as He moves within His creation and especially within those He has called to perform a special work or to understand their new life in Jesus and the life of salvation we are to live.
God sent His spirit into several craftsmen to perform the roles of building the tabernacle exactly according to His instructions. Ex 28:3, 31:3
When we read 'he' or 'him' when referring to the Holy Spirit, we don't need to imply another entity to God or a separate entity to the Father. The Holy Spirit is another term for God and spirit is a term for God's presence within man. The gift Peter speaks of is that spirit of God that would inspire and convict of sin and draw people into relationship with God by knowing His will for them.
We have a spirit in us as humans - it is not a separate entity to us, it is our intelligence and humanity that makes us different from animals.
Jesus too was given the Holy Spirit before his temptation in the wilderness - he could not rely on his own resources as a man to avoid sin. So we too need God's gift of spirit to avoid sin and overcome - just as Jesus did.
But take heart! I have overcome the world. John 16:33
The Holy Spirit is the power of God. This is how Mary became pregnant - not by another entity to the Father God, because He is Jesus' Father - not the spirit.
This power was responsible for allowing miracles to occur via the hands of the Apostles - when the people saw these things they marvelled. Simon wanted to give this power to others too so much, he offered to buy the privilege. That's not how God operates and he was given a stern warning.
Without God's spirit in us, we have no idea about the things of God. When we begin to seek God's way in our lives, He has been at work already as no one can come to God without Him intervening first. So, whether we see the results of God's spirit in others or we are inspired by the bible's words, we might seek to have His spirit in greater measure and seek to know God more in our lives.
In this life Christians are given only a deposit of spirit so we can begin to alter our lives for God's purposes. When Jesus returns, God will grant the faithful a new life of spirit which will grant us immortality with Him.
(God) put His spirit in our hearts as a pledge of what is to come. 1Cor 1:22
That is the short answer.
