Why does the author make reference to keeping the socks in a birdcage and feeding them?

In the Pablo Neruda poem "Ode to My Socks," the speaker utilizes a number of analogies to emphasize the value he places on this particular item. The speaker is not saying he literally wants to put the socks in a birdcage and feed them birdseed and melons. The first thing you should look at is the beginning of the stanza. The speaker tells us that it is a temptation that needs resisting—he is trying to resist the urge to protect and worship these socks because they're so wonderful. He then provides a litany of examples of how he could idolize them but won't.
Imagine for a moment what a "golden cage" might look like and the type of glorious bird that might reside in it. The speaker is saying that he would like, among other things, to put his socks somewhere special, beautiful, revered, and sacred to keep them safe and demonstrate how precious they are to him. Ultimately, he chooses not to. The beauty of the socks, the "twice beauty" he identifies, is that they are functional—because they are meant to be worn.