Yesterday in our harmony lesson with Victoria we analyzed the hymn setting Wondrous Love.
It doesn't have any accidentals next to the clef and ends on the D minor chord. That's why it's not a D minor key but Dorian mode with raised 6th scale degree.
It turns out that Dorian mode was still common in Bach's time. You might remember his Dorian Toccata:
By the way, here's Vidas' video about the ancient modes I thought you'll enjoy watching:
Demonstration of the Diatonic Modes (Vidas Pinkevicius)
Let me know if this helps.