In the New Testament, there are (at least) three theologies at work, and in conversation with each other:
Peter & James:
Be good Jews; Faith without good works is a dead faith. Do the right thing ethically; Deep sense of how suffering brings us to a closer relationship with Christ. Organizationally rigid.
• Letters: James (probably written by James), 1 Peter (probably not written by Peter)
• Gospels: Matthew, Mark
Mystical, spiritual experience; phrased in Greek philosophical language; tradition doesn’t matter; highly developed Christology; no other authority but Logos/Christ acknowledged. End-times apocalypse flavor. Ritual: baptism, tongues, joy. Much eucharistic language, deep mystical meanings suggested, but curiously, no account of the Last Supper. Possible association with Apollos. Institutionally not very organized (maybe even anti-organization).
• Letters: 1, 2 John. Not sure about 3 John or the very strange Jude
• Gospel: John
Faith alone saves us. No need to be Jewish. Christ dwells in each of us and we in him; all of us are given gifts by the Spirit to use bringing the Reign of God to Earth. Practical solutions to practical problems; downplay of apocalypse – we will be here for many years. Highly organized but flexible for local circumstances.
• Letters: by Paul or associated with Pauline followers: Romans; 1, 2 Corinthians; Galatians, Ephesians, Philipians; 1,2 Timothy, Titus, Colossians, 1, 2 Thessalonians; Philemon, Hebrews, 2 Peter.
• Gospels: Luke/Acts of the Apostles