Revelation 19:10 says:
“Then I fell down at his feet to worship him, but he said to me, “You must not do that! I am a fellow servant with you and your brothers who hold to the testimony of Jesus. Worship God.” For the testimony of Jesus is the spirit of prophecy.”
When John falls at the feet of the angel, he rebukes John, telling him to worship God alone. God has spoken through the angel, but God also speaks through John and other Christians. The angel is merely a “fellow servant” with John and his fellow Christians who hold to the testimony of Jesus. This is “the spirit of prophecy”. That is, John and all Christians who bear testimony to Jesus are also proclaiming the word of God, just like the angel. Testimony to Jesus is the spirit of prophecy.
Often we think of prophecy as some sort of futuristic prediction. We can be quite self-centred, thinking that prophecy is a proclamation of what God has in store for me and my life specifically in the future. Of course God could tell us such things. However prophecy in the Bible very rarely works like that.
Prophecy in the Old Testament is rarely about predicting the future (although that does happen). Usually prophets speak to the people of their own time and call them back to the covenant God made with them at Sinai. However they also look forward. All the Old Testament prophecies are fulfilled in Jesus (Luke 24:25-27; Luke 24:44-46; John 5:39; 2 Corinthians 1:19-20). The Old Testaments prophets look forward to the ultimate fulfilment of their words in Jesus. Thus the spirit of prophecy is testimony to Jesus. The prophets spoke about Jesus and their words point forward to him and are fulfilled in him.
In the New Testament it is the same, but we point back to Jesus. The gospel declares the person, life, death and resurrection of Jesus Christ. Thus the spirit of prophecy is the testimony of Jesus. Prophecy points to Jesus, whether it points forward or backwards.
Prophecy then is not so much about us, it is more about Jesus. It is declaring the gospel: bearing testimony to Jesus.
There are what seem to be exceptions to this: often Agabus is mentioned
(Acts 11:28-30; Acts 21:10-11). However most prophecy in the Bible is not so specific and predictive; Agabus is an exception to the general rule. And furthermore Agabus isn’t just making some prediction about any old individual. These are major movements in the early church regarding the apostle to the Gentiles and the survival of the Jewish church from famine.
I’m not saying that what I have written here exhausts the subject of prophecy. However prophecy is primarily about Jesus. The spirit of prophecy is the testimony to Jesus. Do you want to prophesy? Then tell people about Jesus!