Years before Christ came, the prophet Joel prophesied about the pouring out of the Spirit. There were many occasions in the Old Testament before Joel in which certain individuals were filled or anointed with the Holy Spirit. Joel prophesied,
[Joe 2:28 ESV] "And it shall come to pass afterward, that I will pour out my Spirit on all flesh; your sons and your daughters shall prophesy, your old men shall dream dreams, and your young men shall see visions."
I think that it is important to point out that the Spirit is to be poured out on "all," and also it is important to note that each time in Scripture when the Spirit is poured out something happens (whether it be tongues as frequently demonstrated in Acts or here it indicates that prophesy, dreams, and visions. Other times we see bold preaching). The point is when the Spirit was poured out it was experiential. I don't think that anyone can experience the filling of the Spirit without knowing that it happened.
In the New Testament, the pouring out of the Spirit becomes clearer. The Spirit could not come in fullness until Jesus was glorified. John writes,
[Jhn 7:39 ESV] "Now this he said about the Spirit, whom those who believed in him were to receive, for as yet the Spirit had not been given, because Jesus was not yet glorified."
So Jesus had to be glorified before the Spirit was fully poured out. Later, after Jesus was glorified, Luke writes in Acts,
`[Act 2:16-18 ESV] "But this is what was uttered through the prophet Joel: "'And in the last days it shall be, God declares, that I will pour out my Spirit on all flesh, and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams; even on my male servants and female servants in those days I will pour out my Spirit, and they shall prophesy.'"
There it is, a direct interpretation and fulfillment of the prophesy of Joel. However the need for the power of the Spirit continues today. The gift of the Spirit was not prophesied a long time ago so he could be poured out for a couple of days, or months, or years. The gift of the Holy Spirit is for us today. Jesus has been glorified and we are able to receive his gift. Why would the gift of the Spirit be prophesied by Joel, reiterated in the Gospels, poured out in Acts, and then become a historical story that we retell as if it were the good old days? In other words was the Spirit only for the early church? Of course not.
Scripture goes on in the epistles to tell of the Spirit's powerful work in churches in various cities. The disciple did not stand up with Jesus in his suffering but instead abandoned him. Even after Jesus' resurrection, he appeared to them and told them to wait for the Spirit. Then they hid in the upper room until the Spirit came. However they were transformed when these same disciples were baptized with the Spirit and then began to boldly proclaim the cross. They were now willing to suffer for Christ.
We need this transformation, and we need this power. Really we can't accomplish anything spiritual without the power of the Spirit anyway. Let us seek the power of the Spirit and not be afraid to experience the comfort, work, and gifts of the Spirit daily as we are witnesses of Christ.