Rashi on Exodus 23:17/רש"י על שמות כ״ג:י״ז

1שלש פעמים וגו׳ THREE TIMES etc. — Because this section speaks mainly of the Sabbatical year, it was necessary to state that the sequence of the festivals should not be disturbed even in this year of agricultural rest (Mekhilta; cf. Rashi on v. 12).

2כל זכורך means all the male population among you.