1. A call to the celebration 81:1-5

81:1-2 Asaph summoned the Israelites to sing joyfully to God their strength with musical accompaniment.

81:3-5 He called on them to participate in a festival. The Israelites blew trumpets and offered sacrifices at the beginning of each new month, and each month began with the new moon (Num. 10:10; 28:11-15). The Feast of Tabernacles was a joyous occasion that began on the fifteenth day of the seventh month (September-October) when the moon was full (Lev. 23:33). God required the Israelites to observe these occasions. He began to specify these national festivals when He gave the Israelites instructions concerning the Passover (Exod. 12). This instruction was completely new to the nation as though it was a voice they had never heard before.