When you hear an expert in his field talking with another person who is equally qualified in the area, the conversation is usually not understandable by the average man or woman. They discuss concepts and use terminology that you have never known! But if you apply yourself to study and learn, then the things that made no sense become clear and understandable.
Jesus is telling us that even as a follower of His there are things that He would like to tell you, but you are not ready to understand. It is the Holy Spirit living in you, who shows you what is true and guides you into the full truth!
If you think that right now you "know it all" when it comes to the things of God, then you are mistaken! Every day as you walk with Jesus and are filled with the Holy Spirit you come to know more of what He wants you to understand.
Then Jesus says something that is truly remarkable. He says that the Holy Spirit "will let you know what is going to happen!" So the best place to determine what the future will bring for a follower of Jesus is to ask the Holy Spirit to let you know! You can spend all your time listening to men and women who think they know what the future will bring, or you can focus your attention of the Holy Spirit and He will tell you the truth about the future!