As a Pharisee, Paul was an expert in Jewish law. As he reforms his theology around Christ, he doesn’t throw away the entire Hebrew body of scripture. Instead, he takes what he knows of Old Testament and uses it to frame Christ as the completion of that promise. What Moses had, we now have as believers in Christ. The Spirit that rested on him but faded after a time lives with us continuously. For a Pharisee like Paul, this was like hitting the jackpot.