1 Peter 1:12
It was revealed to them that they were serving not themselves but you, in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look. (ESV)
There are three groups of people in this verse. The Old Testament prophets, the New Testament preachers, and the angels from heaven. There are also three time periods represented in this verse. The prophets were from centuries before Christ. The preachers were in the first century AD, and the angels are from time before all the people on Earth were born.
The prophets were preaching to the people of Israel of a coming Messiah, Jesus Christ. They spoke of things that they would never see. None of the Old Testament prophets actually got to see their prophecies come true. They spoke of the grandness of the coming Savior. They gave people of Israel hope as they looked forward to the one who would come from heaven and pay the penalty for sins.
The preachers of the New Testament spoke of their own experiences of Jesus Christ. They were eyewitnesses of his glory. They also preached of how Jesus fulfilled all of what was said of him by the Old Testament prophets. Once again we see this concept of how Jesus Christ was in the Old Testament concealed and in the New Testament revealed.
The last thing we see in this verse is a reference to angels. Peter says that the "things" concerning salvation are what angels long to look into. We know very little about angels. We know that they are God's messengers. Here we get direct insight into what they are excited about. They long to look into our salvation. We will someday know how much of a help they have been to us in our lives.
Remember your salvation. It is something that should be on your mind every day of your life. Don't let angels have more interest in your salvation than you do! Praise the Savior for your salvation that was prophesied about, preached about, and pondered about.