Moses
Leviticus 23:21BSB·traditional attribution

On that same day you are to proclaim a sacred assembly, and you must not do any regular work. This is to be a permanent statute wherever you live for the generations to come.

Matthew Henry Presbyterian @wholebiblehenry

Here is the institution of the feast of pentecost, or weeks, as it is called (Deu 16:9), because it was observed fifty days, or seven weeks, after the passover. It is also called the feast of harvest, Exo 23:16. For as the presenting of the sheaf of first-fruits was an introduction to the harvest, and gave them liberty to put in the sickle, so they...

Commenting on Leviticus 23:15-22

John Gill Reformed Baptist @doctorgill

And ye shall proclaim on the selfsame day, that it may be an holy convocation unto you,.... This proclamation was made by the priests with the sound of a trumpet, that the people might observe that this fiftieth day, or day of Pentecost, was devoted to sacred service, and that they were called to holy exercises in it: ye shall do no servile work therein...

Jamieson-Fausset-Brown Reformed @jfbcommentary

FEAST OF PENTECOST. (Lev 23:15-22) ye shall count unto you from the morrow after the sabbath--that is, after the first day of the passover week, which was observed as a Sabbath.

Commenting on Leviticus 23:15-22