According to the bible, the "spirit of prophecy" is the...
The testimony of Jesus is the spirit of prophecy.
In the 19th chapter of Revelation, John was mistakenly about to worship an angel which the angel corrected him and then said.....
Revelation 19:10
New King James Version
10 And I fell at his feet to worship him. But he said to me, “See that you do not do that! I am your fellow servant, and of your brethren who have the testimony of Jesus. Worship God! For the testimony of Jesus is the spirit of prophecy.”
Jesus Christ fulfilled all the Law of Moses while on the Earth and is also fulfilling all that the Prophets have spoken or written. The testimony of everything that Jesus has done, is doing and will do is evidence that Jesus Christ is fulfilling all prophecy which fulfills the Father's Will in It's entirety.
Jesus Christ testifies of the Father and we testify of Jesus Christ because the Holy Spirit gives understanding and makes all the Father's Will and Jesus fulfilling the Father's Will known to us and the angels of heaven.