And. . . It can be noted that "things" are usually liquid, but the concept of "sea" as "abundant" and the poetic use of "the" ("article in feminine") already suppose that it can refer to a large number of any issue or matter.
Colloquial expression the sea of beautiful, very beautiful. "The sea of" indicates a lot of something, usually good or positive. It also expresses intensity in some quality or characteristic, often with adjectives or adverbs, as in the sea of good.