Surfing around the biblio blogosphere, I saw a comment by Michael Bird about Romans 7 being one of the hardest NT texts to interpret. That got me thinking: what are some of the hardest texts?
Romans 7 is surely difficult, but I'd place 1 Cor 15:29 ("baptized for the dead") as more puzzling. Also, 2 Thess 2:8 (restrainer), Luke 22:36 (why do they need a sword), Mark 16:16-18 (the teaching on baptism and snake handling ... if it's original which I don't think it is), John 1:16 ("grace upon grace"), 1 Cor 11:16 (is it a practice in the church or not), Romans 11:26 ("all Israel will be saved"), Matthew 16:18 (is Peter the rock), John 20:22 (Johannine Pentecost?), and 1 Pet 3:18-21. Also, the divorce texts can be very frustrating when attempting to apply them to real life church situations. Any others you'd like to add?
Also, how about passages that are frequently mutilated? Like lukewarm Christians in Revelation 3:15-16 or "stumbling block" theology (Rom 14; 1 Cor 8) or 1 Thess 5:22? Those are really not difficult passages, but they sure are mishandled a lot.