The setting sun returns to the mountains and seas, what does it mean that mountains and seas hide deep meanings?

"The setting sun returns to the mountains and the sea" means that when the sun sets, if you stand on the mountainside or the seaside and watch it, it will feel like it gradually disappears into the mountains or the sea. "Mountains and seas hide deep meanings" is a metaphor. The mountains are so tall and boundless, and the sea is so vast and boundless. The meaning is difficult to figure out.

The first couplet uses a contrasting technique to point out the place of farewell and depict the beautiful scenery of mountains and rivers; the chin couplet expresses the poet's deep concern for his friend's wandering life; the neck couplet uses "floating clouds" to compare with the friend's whereabouts, and the "setting sun" The expression expresses the feeling of farewell; the last couplet says that Zebra cannot bear to see the scene of separation, let alone between friends who have deep love and righteousness.