기에

Because, given that

Gives a reason, in a slightly weightier and more written way than everyday speech: because it was the final performance, because you were all there, because this place existed. On a verb of perceiving it becomes 'to my mind' or 'as he sees it' — one line opens with 'in my opinion', another with what Min Sik feels. Squeezed with 는 into 기엔 it means 'for something that is X' — the line calling a side dish too good to be a side. 니까 gives a reason too but sounds ordinary and spoken; 기에 sounds composed.

Register: slightly formal, written-leaning