The Holy Spirit was able to speak to Peter about the salvation of the Gentiles because Peter had made himself fully available to the work of God. You may be a Christian – your sins are forgiven, and you live a holy life. But have you devoted your life to the work of the gospel? Will you put everything on the line for revival? It's clear from the scriptures that Peter didn't fully understand everything, he simply understood and was willing to fully give himself to Jesus for whatever purpose(s) that may entail. Are you willing to do the same thing he did?