I wanted to give air to an idea that has captured my thoughts from time to time. Today people talk blithely of the Holy Spirit and ascribe to it this wonder and that duty, but there is a decided lack of appreciation for its effect on early Christianity.
We live in a faith tradition where the Holy Spirit is a commonplace article. We are familiar with it as one of the many gifts of God. What we don't take into account is that the people of God did not always have it. We read our New Testaments as though they were textbooks describing this or that function of the Spirit without fully realizing how profound of a change the advent of the Spirit was to the earliest Christians.
For centuries prior to Christ, the "Spirit of God" was said to have been silent. The idea of being "in the Spirit" referred to occasional divine revelation or provocation to do or say something. Christ refers to David speaking while "in the Spirit" in Matthew 22:43. Other examples are presented in Luke 2:27 and Acts 19:21. It was exceptionally rare both in terms of possessing people very rarely and in terms of only possessing people for a limited amount of time.
It had to be shocking, utterly shocking, then for early Christians to find out that, in the new covenant, EVERYONE could have the Spirit ALL THE TIME. I don't think we really appreciate how significant a change this was to their views on God's providence. I further believe that the more we realize this, the more we can find in the Bible indication that the sending of the Spirit was considered the gift obtained by Christ's work.
Christ refers to it as "what was promised," and that term "promise" is used several times in Acts to refer to the Spirit. The term "gift" is practically synonymous with Holy Spirit throughout the teachings of the apostles in Acts. John's account has Jesus saying that the Spirit's advent was contingent on his death. Once your eyes are open to it, these types of allusions show up all over the place.