Both celebrations were definitely intended to extend the Christmas holidays, just like Easter Monday is used to elongate the Easter celebrations in both nations. However, both sacred and secular notions are tied to this day.
From a religious perspective, the Early Church decided that the days immediately following the birth of the Son of God should be dedicated to the “comites Christi”, or the saints closest to Jesus in his journey on Earth, and the first to give their lives for the Christian faith. Most likely a Jew educated in Hellenistic culture, Saint Stephen was the first Christian martyr, the first to die in the name of his faith and for spreading the word of the Gospel.
On the other hand, various theories surround the origins of Boxing Day, celebrated in Commonwealth countries such as the UK, Australia, Canada and New Zealand. Many believe that the name derives from the need to clean the house and throw out the boxes which contained presents received on Christmas Day. In reality, it has nothing to do with that. Today, this celebration is tied to sales and “wild” shopping, but originally it was quite the contrary: it was about giving, not taking. In Great Britain, the day after Christmas was a time to donate money or goods to people of lower classes. Even employers would pay their staff an extra sum of money, and rich merchants would offer crates of food to smaller traders or servants who worked for them. This custom was so common that it became an unwritten rule.
But why the name Boxing Day? It was because, during that time, gifts in the form of money or goods were contained in boxes which varied in size depending on the contents. The “box” was basically an ancestor of modern Italy’s “tredicesima” (an extra pay packet at the end of the year), or the “Christmas bonus” given out by some Australian companies. Therefore, Italians may interpret Boxing Day as “il giorno della tredicesima”!