The speaker begins with a plain admission: they don't yet understand the sea. The title, "Oceanologist," makes that confession a little ironic, since an oceanologist is supposed to be someone who studies the sea and knows it. Here the expert is still a student, humbled before something too big to grasp.
The rest of the poem seems to describe the sea as a "cunning fellow" who can "put on several faces." That fits how water changes, from calm to rough, from bright to dark. The speaker then asks a question: what kind of world would it be without this kind of disguise, a world where you could meet a cliff and simply laugh? The sea, it seems, can shift its manner, but a cliff is solid and cannot hide anything. The image of laughing at a cliff is odd and a bit playful, and the poem doesn't spell out exactly what it means. The mood is curious and wry, with a quiet respect for something that won't be pinned down.