Why did he say "v'Yaradta Lefanai"?
Rashi: You descended, and afterwards I will descend.
What is the meaning of "Tochel"?
Rashi: Wait.
When do the seven days [of waiting] begin?
Radak, Malbim: It is from when Shmuel departed after Chidush of the kingship, for which both came together to Gilgal, with all of Yisrael. 1
Radak: Why did Shmuel command him now, and not at Gilgal? He hinted to him that through this, his kingship will last. This was the first Mitzvah that Shmuel commanded him [after becoming king].
What will Shmuel tell Sha'ul to do?
Radak: He will tell him whether or not his kingship will last (based on whether or not he kept his first Mitzvah, to wait seven days).
Malbim: It is regarding the war with Pelishtim. I told you to do as you can - but in Gilgal, you may not do anything without me.