ויקהל משה… ששת ימים תעשה מלאכה… (ויקהל לה:א-ב)

Why does it say “ויקהל משה” – Moshe Rabbeinu assembled and not “ויאמר משה אל כל עדת בני ישראל” – and Moshe said to the entire assembly of Yidden? 

By using this specific word “gathered” when Moshe Rabbeinu is talking about the holy Shabbos, the Torah teaches us that the days of rest – Shabbos and Yom Tov – should be used for gatherings, during which the Rabbis should teach their congregation the holy Torah.