Lentils are eaten in Italy on New Year's Eve and New Year's Day as a symbol of coins and prosperity. Their small, round shape is traditionally compared with money, so eating them is associated with hopes for financial luck.
The dish is commonly served with cotechino, a seasoned pork sausage, or zampone, a stuffed pig's trotter. Pork has its own prosperity symbolism in several European traditions because a pig's forward rooting suggests progress and abundance.
The lentil custom is one part of Italy's varied regional New Year's food traditions. It is not a rule that every Italian household follows in exactly the same way. The practice is also related to broader European beliefs that certain foods consumed at the year's turning can influence fortune, although the foods differ from country to country.