Shabbos 30a: A human king makes decrees and it is in doubt if they will be followed. And if they are followed during his lifetime it is doubtful they would be followed after his death. However, when Moshe Rabeinu established many decrees they are followed forever.
WHAT ARE THE DECREES OF MOSHE RABEINU?
To expound to the Jews every Shabbos and Yom Tov
Yalkut Shimoni explains that Moshe established this decree in the desert. ויקהל משה (and Moshe assembled) was never said in the entire Torah except in this one occasion. HaShem told Moshe to assemble the Jews to teach them so they can expound for future generations. Therefore, Moshe decreed that every Shabbos the leaders should gather the people to teach them the applicable laws of the day (Shabbos laws on Shabbos, Pesach laws on Pesach, etc.)
To read from the Torah on each Yom Tov about the matters of the day
Rambam specifically states the Moshe decreed this matter
The blessing of Hazan (first blessing of Bircas haMazon after eating bread)
Berachos (48b) specifies that Moshe Rabeinu established the first blessing in honor of the Mahn that fell from Heaven.
Appointment of Mishmaros for the Cohanim
Taanis (27a): Moshe established groups for the Cohanim for service in the Mishkan; four from Elazar and four from Isamar. Later Shmuel apportioned the Cohanim into 16 groups and eventually Dovid established 24 groups. One group did the service per week in the Mishkan and Bais HaMikdash, with a rotating system.
Format of Prayers
Yoma (69b): Moshe established the basic format of the prayers per "הא-ל הגדול הגבור והנורא"
Reading the Torah in public settings
Yerushalmi Megilah (29a): Moshe established that the Jews should read publicly from the Torah on Shabbos, Yom Tov and Rosh Chodesh, as it says "וידבר משה את מועדי ה' אל בני ישראל". Per Rambam Moshe established the public reading on Shabbos, the second and fifth days of the week so that three days would not pass without the public reading of the Torah.
Seven days of festivities of marriage and seven days of mourning
Yerushalmi Kesuvos (2b): Moshe established these periods of time.
Making 100 blessings a day
Chida: Tradition that Moshe established the decree that everyone should say 100 blessings a day. The decree faded and was forgotten until the time of Dovid who reestablished the decree (after 100 people were dying each day). Megaleh Amukos states that Moshe established this decree when he gave the 100 sockets (אדנים) to the Mishkan.
Chinuch of children
Netziv: Moshe established in his generation the mitzvah of training children in Torah and Mitzvos.
Netziv tells us that Moshe was the father of those that established decrees (גודרים). Thus, one of the names of Moshe (he had 10) was Avigdor, ביגדר.
