We distinguish among various different works attributed to the Third Person of the Trinity.
For example, regeneration is so vitally important, and the Holy Spirit is the One who changes the disposition of our hearts. Anyone who was a believer in the Old Testament had to be regenerate before they would be a believer. So anyone who was regenerate the Old Testament experienced the work of God the Holy Spirit in changing the disposition of their soul.
We also talk about ways in which the Holy Spirit filled people. The first people we read about being “filled” by the Holy Spirit in the Old Testament, strangely enough, were those whom God called to be artisans for the construction of the tabernacle (Ex. 31:1-6; 35:30-36:2). They were gifted by God the Holy Spirit in order to fulfill that particular task.
You also see that other offices and operations of the Holy Spirit in the Old Testament saints included a particular charismatic anointment or empowering, like the prophets whom the Holy Spirit came upon, and the kings who were anointed by the Holy Spirit.
You go back to the book of Numbers and you see where Jethro, the father-in-law of Moses, rebuked Moses for doing too many things by himself. He was led by the Lord to instruct Moses, and he said, “Gather seventy of the people that you know are elders among the people, bring them to yourself, and I will take of the Spirit that is upon you and distribute it among the seventy” (Num. 11:16-17). That’s recorded there in the Old Testament. So, the multiplication of the empowering of Moses was given.
And at that time, when Joshua raised up a question about it, he said, “Moses! Eldad and Medad are prophesying in the camp. Please forbid them.” And Moses replied, “Envious thou for my sake, Joshua? Would that all of God’s people would be prophets, and He would pour His Spirit out upon them” (Num. 11:29).
That prayer of Moses later became a prophecy by Joel that, in the latter days, God would pour out His Spirit upon all believers (Joel 2:28-29). That’s the significance, I think, of what took place at Pentecost. Pentecost saw the Spirit of Christ distributed, not just for seventy people to empower them for ministry, but to the whole Christian community (Acts 2:16-21). All believers received the Holy Ghost and were empowered (Acts 2:38).
Now I know that not everybody believes that aspect, as we’ve seen all kinds of controversies about the role and the person of the Holy Spirit in our day. One of the best studies that you can ever get is the study by Sinclair Ferguson on the person and work of the Holy Spirit. So, I commend that to you.