Romans 9:23

And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,

God makes known the riches of his glory through the vessels of mercy, those who receive his mercy and whom he prepared beforehand for glory. Those prepared for glory are those he has called, and they include people called from among both the Jews and the Gentiles. His purpose in this calling is to reveal his grace among both peoples.

The verse does not teach that God delights in tormenting the wicked forever while the redeemed look on with approval. To be a vessel of mercy does not mean the saints are made happier by witnessing the endless suffering of others. Nor does it mean they are expected to praise God for such suffering.