The Holy Spirit is active during the Old Testament. At creation, we find that the Spirit of God is hovering above the waters. During the exodus from Egypt, the time of the first kings, and most notably during the ministry of the prophets, the Holy Spirit is active. But despite the wide ministry of the Holy Spirit during all of this period, what the Old Testament believers saw was just a small deposit of what was to come.
For example, in Numbers 11:17 we read that “God will take of the spirit that is on you [Moses] and put the spirit on them.” (The “them” are Israel’s elders.) God did exactly what he promised, and “when the spirit rested on them, they prophesied, but they did not do so again.” (11:25) The narrator goes on to tell us that two elders, Eldad and Medad, were not with the others. “Yet the spirit also rested on them, and they prophesied in the camp.” Moses, brushing aside Joshua’s concerns, exclaimed, “I wish that all the Lord’s people were prophets and that the Lord would put his spirit on them!” (11:29)
This vignette from the Pentateuch illustrates perfectly the nature of the Holy Spirit’s presence in the Old Testament. 1) The event is exceptional: the Holy Spirit came on little more than a few hundred men in the thousands of years than encompass the Old Testament. 2) The event is transitory: the Holy Spirit came, then went.
And yet there was a hope (you might say a prophecy), that one day all of the Lord’s people would be prophets and the Lord would put His Spirit on them.