The speaker talks to someone whose heart is like an old songbook, its pages stained by years of experience. The song is beautiful, but the words are hard to make out, and the heart seems to be locked away behind walls of cold steel. The speaker can't read it or hear it clearly, and that frustrates them. They keep asking what the heart sings of, and what it cries for.
What stands out is how determined the speaker is. They promise to learn every rhyme and every dance step, to chant until they run out of breath, and to find whatever or whoever the other person is missing. The imagery of magic, spells and "abracadabra" makes this feel like a quest to free someone from a curse.
The mood is tender, hopeful and a little desperate. By the end it becomes an offer of friendship or love: sing to me, and I will understand you completely.