The thanksgiving offering was brought by someone who had (for example) survived great danger, escaped captivity or recovered from a grave illness. The offering was accompanied by 40 loaves of four different types of bread (Leviticus 7:12, Talmud Menachot 77b). This resulted in an enormous amount of food which had to be eaten on the day that the offering was brought.
It was therefore essential that someone who was obligated to offer thanks to God in this manner invited others to partake of the offering. In turn, this gave the "host" the opportunity to share and publicise their gratitude to God with friends and relatives.
Rabbi Aryeh Leib ben Asher Gunzberg (died 1785), in his magnum opus Shaagas Aryeh, explains that the requirement to consume the entire offering in one day also teaches us that the blessings God bestows on us are not reserved for happy occasions, but are ever-present and benefit us every day.
It is natural to want to share the happiest events in our lives with our friends and family. Whether we are celebrating the birth of a child, a bar/batmitzvah or wedding, we publicise our gratitude to God by sharing our simchah (happiness) with others.
Nevertheless, we must be mindful and grateful for even the simplest of blessings which often go unnoticed in the daily humdrum, but are nonetheless there: the blossoming of the trees in springtime, the laughter of our children and grandchildren, the constant, unconditional love of our families. If we could slow down a little from time to time, we would begin to appreciate the myriad of blessings which envelop us and carry us through each day of our lives.
Rabbi Dr Moshe Freedman