The more ancient odes were written about epic characters and events. The Romantics (Keats, Shelley) wrote odes about elements of nature (Nightingales, Seasons) which provided a means for them to consider transcendent experiences. In this poem, Neruda is praising a very simple, common thing: his socks. He describes them in terms not usually associated with socks: as "knitted with threads of twilight" (or dusk, depending upon the translation). Twilight (dusk) is the transition from day to night, when there is still a glow from the sun which has just set. That is to say, the socks were formed by this mysterious glow that exists between two times: night and day.
His feet are "honored" by these socks, as if the socks imbue his feet with life, becoming like "woolen fish" and "blackbirds" with the power of canons. He is humbled by these gifts (from Maru Mori) and feels that his feet are not worthy. This poem has all the form and language of an epic ode, but is about socks. And there is a reason for this.
The speaker (Neruda) clarifies that he will not keep the socks like some Holy Grail or some object in a museum. That is, he will not treat them like some sacred object that is worth only what it symbolizes. He resists treating them like captured fireflies, like the "sacred documents" of scholars, or like animals in a "golden cage." This is not an ode to some object that is "objectified" and praised only for its symbolism or outward appearance. This is an ode to something that is useful every day. In comparing his socks to these sacred objects, the speaker concludes that his socks are twice as valuable as those sacred things:
what is good is doubly
when it's a matter of two
The literal meaning is that they are doubly good because there are two of them. But they are also doubly good, twice as good as, say, a sacred object because they are practical and symbolic of warmth, and generosity (being gifts). This is a poem about finding the extraordinary in the ordinary. Neruda celebrates the beauty of the utility of his socks.