I just read an article about a Muslim who became a believer after Jesus appeared to him in a dream or vision saying "I am Jesus, follow me". When Hebrews says that God the Father now speaks through His Son, does that mean in the testimony of scripture or can Christ appear to people in their dreams too?
The Lord continues to accomplish miracles as suits Him to reach the unreached, including bringing dreams to muslims in countries that are closed to the Gospel. These miracles occur under circumstances similar to the early church, when the word of God was not yet available (as the canon was yet to be written), and so the Lord gave his apostle’s the ability to perform miracles so as to substantiate the message they delivered. This still happens on rare occasions in areas of the world where the word of God is not available.
Once the word of God is available within an area of the world, however, then the miracles cease (as they did generally after the first century) so that the word of God is honored above signs and wonders. Faith comes by hearing and hearing by the word of Christ, not by signs and wonders. To learn more about these things, we recommend you listen to our Acts and Romans Bible studies.