There is actually authority from the scripture which explains that statement, (not me, but the scripture), in fact, from the same author; and if any would receive it the passage reveals that the Testimony of Messiah is what is finished when the Master says that at Golgotha. Thus the Testimony of Messiah is itself the "new covenant Spirit", (because testimony is spirit whether for the good or whether for the evil). This may be understood by a simple reading of the following passage without adding any words to it like most English translations do. I have found that from the English renderings the Young's Literal Bible Translation is one of the very few which actually renders it without adding the word
"given" into the text. That word, (the Greek equivalent), is not found in any codex or manuscript even though most English renderings incorrectly insert it into the text because they do not understand that the Testimony of Messiah is actually the new covenant Spirit, (meaning that to have "the Spirit" one must actually be IN the Testimony of Messiah to be "IN Messiah", actually DOING his teachings and commandments, and not just claiming some ethereal presence for having made a one-time confession of "faith"). Read the following and understand that when the text says "Jesus was not yet glorified" the author means lifted up at Golgotha, (glorified being the same as exalted or lifted up).
And do not add "given" into the text because it does not belong there:
John 7:37-39 YLT (Young's Literal Bible Translation)
37 And in the last, the great day of the feast, Jesus stood and cried, saying, 'If any one doth thirst, let him come unto me and drink;
38 he who is believing in me, according as the Writing said, Rivers out of his belly shall flow of living water;'
39 and this he said of the Spirit, which those believing in him were about to receive; for not yet was the Holy Spirit, because Jesus was not yet glorified.
There it is as plain as day:
"For not yet was the Holy Spirit, because Jesus was not yet glorified", (at Golgotha).
The "new covenant Spirit" is the Testimony of Messiah, and it was not finished until Golgotha when the Master cried out, "It is finished", meaning his full Testimony; which if we observe, heed, do, and carry out in our own walk, is our sanctification and our salvation because it is the soterion-peace-offering that reconciles us unto the Father.