The prophet Joel spoke of the destruction of Judah, the exile, and the days of refreshing when God would be in their midst and pour out His Spirit upon the people. This is the primary passage speaking of the prophesying to come as part of that event. Rejuvenation, Revelation, Cleansing salvation are the main reasons the Spirit would come.
God is spirit and He is the source of our spirit.
The word Spirit is comprised of two words in the old and new testament. In the Old Testament it is the Hebrew word – ruah. In the New Testament the Greek term is – pneuma. These are regular terms that mean breath.