Jesus best describes the difference between the Spirit’s role in the OT and NT economies.
And I will ask the Father, and He will give you another Counselor to be with you forever. He is the Spirit of truth. The world is unable to receive Him because it doesn’t see Him or know Him. But you do know Him, because He remains with you and will be in you (John 14:17).
While Jesus was on earth, the Spirit was with His disciples, but not in them. After Jesus ascended to heaven, He sent the Holy Spirit to be in His disciples on the day of Pentecost A.D. 33, and the Church was born. Significantly, Yahweh gave the Ten Commandments on Pentecost 1446 B.C., and the nation of Israel was born. The Holy Spirit empowers the born again believer for living the Law.
From the NT, we know that the Holy Spirit did not continually indwell men prior to Christ’s resurrection and accession to heaven.
On the last and most important day of the festival, Jesus stood up and cried out, “If anyone is thirsty, he should come to Me and drink! The one who believes in Me, as the Scripture has said, will have streams of living water flow from deep within him.” He said this about the Spirit, whom those who believed in Him were going to receive, for the Spirit had not yet been received, because Jesus had not yet been glorified (John 7:37-39).
While He was together with them, He commanded them not to leave Jerusalem, but to wait for the Father’s promise. “This,” He said, “is what you heard from Me; for John baptized with water, but you will be baptized with the Holy Spirit not many days from now” (Acts 1:5).
As promised by Christ, the Holy Spirit came from heaven and filled His disciples on Pentecost, Sunday, May 24, A.D. 33 (Acts 2:1-4). Peter identified this baptism with the Holy Spirit as a partial fulfillment of the prophecy by Joel.
After this I will pour out My Spirit on all humanity; then your sons and your daughters will prophesy, your old men will have dreams, and your young men will see visions. I will even pour out My Spirit on the male and female slaves in those days (Joel 2:29)
Yahweh had first promised this event through Moses.
The LORD your God will circumcise your heart and the hearts of your descendants, and you will love Him with all your heart and all your soul, so that you will live (Deuteronomy 30:6).
The apostle Paul identified this circumcision of the heart as a work of the Spirit.
For a person is not a Jew who is one outwardly, and true circumcision is not something visible in the flesh. On the contrary, a person is a Jew who is one inwardly, and circumcision is of the heart—by the Spirit, not the letter. His praise is not from men but from God (Romans 2:29).