1)
Why did Moshe need to call the people, seeing as he had just told them about the B'ris at Har Gerizim and Har Eival and they were still standing in front of him?
1.
Ramban: "Vayikra Moshe el Kol Yisrael" refers (not to a new gathering, but) to a new teaching that he was about to convey to them.
2.
Oznayim la'Torah: Because the people, terrified of the K'lalos - Refer to 29:68:4:1 0- were beginning to slip away.
