It already said (23:2) that Yehoshua gathered all Yisrael!
Radak: He gathered them again and rebuked them twice, so they will be careful to guard the Torah.
Why did he gather them to Shechem, and not to the Mishkan in Shilo?
Radak: Perhaps Hashem commanded so, so they make the Bris in Shechem, for (a) Avraham delayed there when he entered the land - (Bereishis 12:6), (b) A miracle was done there for Yakov. 1 (c) The start of the inheritance of Eretz Yisrael was there - Yakov bought a field there 2 (Bereishis 33:19). (d) That is where Yehoshua told Yisrael to remove the foreign gods amidst them (verse 23), like Yakov told his sons in Shechem (Bereishis 35:2).
Hashem put fear on the surrounding cities and they did not pursue Bnei Yakov [to avenge killing all the men of Shechem] (Bereishis 35:5). (PF)
Before this, Avraham bought Me'aras ha'Machpelah! Perhaps that is not considered the start of the inheritance, for he bought it for the sake of burial (even though Efron forced him to buy also the field - refer to Bereishis 23:11:1:2,4), or because it was not exclusively for Yisrael (Yakov later needed to buy Esav's share in it - refer to Bereishis 50:5:1:3). (PF)
What is the meaning of "va'Yitzyatzvu Lifnei ha'Elokim"?
