The mystery Paul is talking about is that salvation is provided through Jesus for the Gentiles, and not only to the Jews. The hope of glory refers to the presence of God which is so magnificient that it is really beyond description. Someday we will live continuously in God's presence, after we have suffered here on this earth for "a short time." When we finally live eternally in His wonderful presence our suffering will be only a distant memory, and it will all be worth it. Whenever we are in deep trials, when we seek God desperately with our whole being, He will meet us by sending the Holy Spirit to comfort us and give us a glimpse into what is in store for us someday. Right now we are "looking through a glass dimly", but someday all things will be made clear. Even here on earth, if we seek God's face, He will give us a magnificent glimpse of what is to come, and it brings us great comfort and joy to help bear us up and sustain us through our trials and temptations.