The New Testament is made up of 27 books, each with its own theme. Here's my somewhat reductionistic attempt to summary those themes. I'm sure you can improve them!
Matthew: The long-awaited Messiah
Mark: The Servant of the Lord
Luke: The Savior of the world
John: The Lord of lords
Acts: To the ends of the earth
Romans: Becoming right with God
1 Corinthians: Life in the local church
2 Corinthians: Power in weakness
Galatians: Only one gospel
Ephesians: God's new society
Philippians: Unity through humility
Colossians: Christ is supreme
1 Thessalonians: How to please God
2 Thessalonians: Our coming King
Titus: Good works and the Christian
Philemon: Freedom in Christ
Hebrews: Christ above all
James: Tests of faith
1 Peter: The way of the cross
2 Peter: The promise of his coming
1 John: Living in the love of God
2 John: Living in the truth
3 John: Living in discernment
Jude: The God of protection
Revelation: Heaven revealed