There's an interesting note (with the original text, English translation and audio clip) HERE.

The "Chorus of the Hebrew Slaves", (Va Pensiero), from Verdi's opera Nabucco (1842) attained great political significance. Va Pensiero became the Italians' song of liberation, for, in the oppressed Hebrews, they found a symbol of their own longing for reunification with Lombardy, which was occupied by Austria. The unison chorus (one of the few da capo choruses in all opera) became the underground "national hymn". And the composer's name became V.E.R.D.I, a slogan meaning Vittorio Emmanuale Rei de Italia ("Victor Emmanual, King of Italy") - a reference to the sole native dynasty in Italy and the focus of nationalist hopes for unity.

~Masato