"Concerning this salvation, the prophets who spoke of the grace that was to come to you, searched intently and with the greatest care, trying to find out the time and circumstances to which the Spirit of Christ in them was pointing when he predicted the sufferings of Christ and the glories that would follow." NIV translation
There are many who basically set half of the Bible (the Old Testament) aside and say that it doesn't have anything to do with us today but this passage shows us the truth. We see that God had told the prophets of old about the grace that was coming and they tried to find out the time. We see that God used the Spirit to let them know of these things. God uses that same Spirit in us today and when we look back through history (through the Old Testament) we can grow in our faith as we see what God has done and what He has promised to do.
"It was revealed to them that they were not serving themselves but you, when they spoke of the things that have now been told you by those who have preached the gospel to you by the Holy Spirit sent from heaven. Even angels long to look into these things." NIV translation
The prophets of the Old testament told of the coming of Jesus Christ and they knew that it was for a time in the future. They were serving us in helping us to understand more about God and His plan.
"Therefore, prepare your minds for action; be self-controlled; set your hope fully on the grace to be given you when Jesus Christ is revealed." NIV translation
When you see "therefore" in any part of the Bible, it is always good to go back and review what you have just read. In this case, it is telling us that, because of the salvation that we have, we are to be prepared to act differently. Peter says we are to be "self-controlled" which we are told, (in Galatians 5 by Paul), is a fruit of the Spirit. That tells us that it is from God and that we cannot do it on our own but through the Spirit we can overcome. Peter also reminds us to focus ("set your hope") on the gift of a new life in Christ that we have today (where we can be self-controlled) and a new life when Jesus returns (a life for eternity with Him). We must always remember that it is a gift (that's what grace is).