Sefer Ha’mitzvos Ha’Katzar (the concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
21. It is a positive commandment to be happy on the Festivals
As it says in Devarim (Deuteronomy) 16:14, “And you shall be happy on your Festivals”. When the Beis HaMikdash stood, the happiness was from offering extra Shalomim (Peace offerings) called “Shalomim Simcha” in addition to the Festival Shalomim. Also, women are obligated in being happy. Today, there is no happiness without meat and wine. One is obligated to make his wife happy with nice clothes and to distribute sweets to his children. One is obligated to make poor people happy. One who does not bring joy to the poor does no fulfill the commandment of happiness, only happiness of his belly and this happiness is a disgrace for him, as it says in Malachi 2:3, “I will spread dirt on your faces, the dirt of your Festival.”
Even though eating and drinking on the Festival is a positive commandment, one should not excessively drink wine nor become light headed and joking, since this is foolishness and silly behavior. We are commanded to only have happiness from serving Hashem, blessed be He. It is impossible to serve Hashem through joking, light-headedness, or being drunk, only through fulfilling the joy of the commandment. The happiness that a person has while doing the commandment is a great service to Hashem.
This mitzvah is obligated at all places and at all times.