In verse 4 we have the Spirit; in verse 5 the Lord, and in verse 6 God: these verses are Trinitarian. Verse 5 is a most important statement: the same Spirit.
What confusion there would be if that had been any more than a temporary arrangement. If there were prophets today, it would just be a temptation for a great confusion. How would we know the difference between the true ones and the false ones? How would we know where human imagination was working overtime? We would be at the mercy of human imagination and human ingenuity. No, we have the word of God; it is complete. We can all refer to that, and we can all expound and exegete the word of God. That is the final arbiter of everything for us. The word is sufficient for all our needs.