The latter part of Re’eh describes the three festivals during which the Jew was to go on Aliyat Haregal, to make a pilgrimage to the Bet Hamikdash. An added element is stipulated. The Torah tells us VESAMACHTA LIFNE HASHEM ELOKECHA, “And you shall rejoice before the L-rd your G-d…” (Deut. 16,11) The Torah does not stop with that command but enumerates with whom you should rejoice. It mentions your son, your daughter, your man-servant, and your maid-servant, the Levite, the stranger, the fatherless, and the widow.
The Rambam makes it more emphatic. He says that one who locks the gate to his yard and eats with his children and his wife and does not feed the poor and the destitute, this is not the rejoicing of a Mitzvah but the rejoicing of his stomach.
A person has to share his good welfare and gifts from Hashem with the less fortunate. In this day and age it is not too common to invite the poor into your house on the holidays because they are not necessarily wandering around in the streets at the time of our meals. There are, however, numerous charities and various opportunities through which we can help the poor and the needy to enjoy the holidays as we do.
We are instructed to rejoice on the holidays but we are obliged to see that the less fortunate are also rejoicing. Otherwise, our rejoicing is not the joy of a Mitzvah.