To fully understand the New Testament,----more---- you have to know your Old Testament. It's like trying to understand a joke in a different language. The main difficulty is that you have to grasp the cultural context behind it. The same holds true for everything in the NT.
1. God put Jesus forth as the mercy seat through his faithfulness by his blood. 3:25
put forth: as a priest would present the sacrifice on the altar
mercy seat: where once a year on the Day of Atonement the high priest would enter the Holy of Holies and sprinkle the blood of a bull for the forgiveness of sins for all of Israel for the past year
blood: it is now the sacrificial blood of Jesus that takes care of this and Jesus is now the mercy seat where forgiveness takes place
2. Jews were entrusted with this message from God.
3. But there is no boasting as the message is for everyone.