It is important to distinguish between what old preachers called "the two functions of the Holy Spirit."

In relation to the Everlasting Covenant, he is the agent of regeneration and has been functioning in that role since there was an elect on the earth (Jno. 5:25a -- "The hour is coming and now is...").

In relation to the New Covenant, he assumed a further role as Christ's agent to the church -- the 2nd Comforter, as outlined in Jno 14-16 -- on Pentecost morning. It is in terms of the second "function" that we are to understand passages like Jno. 7:37-39: "...This he spake of the Spirit which they that believe on him shall receive, for the Holy Ghost was not yet given, because Jesus was not yet glorified" (see also Acts 2:38; 5:40). Indeed, there are episodes in the OT in which we read of the Spirit filling, equipping, enabling and encouraging God's people for service. But in this corporate and collective sense as the Risen Christ's agent to the church, he "was not yet given" until the Ascension.