On Sunday after the responsorial psalm a second reading from the Bible is proclaimed at Mass. This reading is always chosen from the letters (you can also say “epistles” if you like) of the New Testament, which really are the earliest Church documents which give witness to our faith.
I'll take this opportunity to complain, then, about what I think is a shortcoming in our clergy's liturgical practice! And I'll admit I'm just as much at fault as just about every other priest and deacon in the world: we don't “preach on the second reading” enough!
Maybe it's because the Gospel narratives tend to be more vivid, while the epistles usually deal with more “dry” theological themes. Maybe it's because the first, Old Testament reading usually echoes a theme of the Gospel, making it hard to ignore two readings while focusing on one. Maybe it's because St. Paul and other New Testament authors were so uncompromising in their challenges! But for whatever reason, most Catholics are woefully “undernourished” on these Scriptures.
How can we combat this? Well, for my part I try to use the second reading whenever I can in my preaching. But one thing all of us can do is read, study and pray over these New Testament letters on our own. Using a “study Bible” guide or at least careful reading of the text will usually prompt a greater appreciation for these Scriptures.