"God who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son."
God spoke through out the Old Testament times. Much of that was recorded for us. He spoke in different ways. All of this can be documented in the Old Testament. I am short on time here so I wanted to focus on the last part of this passage. In these last days [He has] spoken to us by His Son...
"These last days" speaks of the days after the coming of the Messiah. It was written to first generation Christians and subsequently would be passed on to the next generation which would pass it on to the next and so on and so on...to today. Each generation continues in "These last days". This being so, there is no day to come in which God will speak in any other way than through His son as far as revelation is concerned. All God has to say, He has said in Christ. If that is not enough for a person then there will never be anything else that will be authentic for that person to know God by. If you want to know God, get to know the Jesus of the Bible. He is the superior message to all other means of communicating to man. He is superior to angels, He is superior to Moses. He is superior to the law. He is superior to every element of the law.
Hebrews will establish this. But for today, I am grateful to know Christ through the Bible which is living and active...I am grateful and content. I do not need further revelation and do not want to go beyond what is written. This is one reason among many that I reject any so-called modern day "prophet" who claims God speaks to them directly. We have one High Priest, one mediator between us and God, that is Jesus Christ. I do not need another mediator who has a more direct line to God. Jesus is my mediator. All God has to say to me He has said to me in Christ. The entire Bible is Christocentric. God communicates to me by it and all of its connection to my Savior Jesus Christ.