Learn Hardcore Russian: Жених купил невесте кольцо с маленьким камнем, хотя денег было мало. - The groom bought the bride a ring with a small stone, although he had little money.

Breakdown of Жених купил невесте кольцо с маленьким камнем, хотя денег было мало.

Why is невесте in the dative case here?

Because with verbs like купить (to buy), Russian normally uses:

Accusative for the thing bought: купил кольцо (bought a ring)
Dative for the person for whom / to whom it is bought: купил невесте (bought (it) for the bride / bought the bride a ring)

The pattern is: купить (что?) кольцо (кому?) невесте.

So невесте is the dative singular of невеста (bride), marking the indirect object / recipient.

Could we also say для невесты instead of невесте? What’s the difference?

Yes, для невесты is grammatically correct, but there is a nuance:

невесте (dative) – very natural with verbs of giving, bringing, buying; focuses on the recipient:
- Жених купил невесте кольцо. – The groom bought the bride a ring.
для невесты (preposition для
- genitive) – emphasizes the purpose or that something is intended for someone:
- Жених купил кольцо для невесты. – The groom bought a ring for the bride (for her use / for her).

Both are correct, but with verbs like купить, дать, подарить, the dative (кому?) is more idiomatic and a bit more personal.