Question:
In Isaiah 32:15, what does the outpouring of the Spirit mean?

Answer:
Joel 2:28: “And it shall come to pass afterward, that I will pour out My spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions.” This is telling of God pouring out His Spirit and the effects.

Applying this to today: He will use us when we are filled or controlled by the Spirit: “And be not drunk with wine, wherein is excess; but be filled with the Spirit; speaking to yourselves in psalms and hymns and spiritual songs, singing and making melody in your heart to the Lord; giving thanks always for all things unto God and the Father in the name of our Lord Jesus Christ; submitting yourselves one to another in the fear of God” (Ephesians 5:18-21).
Isaiah 32 tells us that what Joel prophesies will occur to the nation of Israel during the tribulation period (verses 9-14) and also during the following 1,000 year reign of Christ over the earth. Verses 16-20 refer to the reign of Christ over the earth during the millennium. (Other verses—Revelation 7:4, 9 and Ezekiel 37:11, 22).So, Isaiah 32:15 primarily refers to Israel during the dispensations that are yet future.