The Holy Spirit in the Old Testament would move on people for specific reasons and would cause them to do things they otherwise couldn’t possibly do. When that purpose was completed, they would be just any ordinary man.
In the NT, the Holy Spirit came not just ON us, but now lives IN us. Furthermore, Jesus came so we would not just be filled with the Holy Spirit, but be baptised – immersed – in the Holy Spirit. God wants something to happen in these days, and we can cooperate with the Holy Spirit to set those things in motion.