Joshua - Chapter 1
This chapter continues the narrative immediately after the conclusion of the Torah in parshas V'zos HaBracha. Accordingly, it is read as the Haftarah on Simchas Torah.
Yehoshua (Joshua) is named the successor of Moshe (Moses) by Hashem. He is commanded to lead the Jewish people across the Jordan River to the Land which G-d has promised them. G-d charges Yehoshua to be strong and brave and to keep the Torah that G-d gave through Moshe. "This book of the Torah shall not leave your mouth," G-d says, "rather you shall be involved with it both day and night." Yehoshua then readies the people, particularly reminding the Tribes of Reuben and Gad and the half Tribe of Menashe of their promise to fight alongside the rest of the nation, despite having received their portion of the Land on the other side of the Jordan (see Numbers 32). The nation affirms that, since G-d is with Yehoshua as He was with Moshe, they will follow Yehoshua as they did Moshe.
Much has been made of the fact that Yehoshua is introduced as m'shareis Moshe, Moshe's attendant. Moshe had two sons, but neither of them was chosen his successor. That role was given to Yehoshua who attended Moshe. In a yeshiva, Yehoshua would have been the student who cleaned up the Beis Medrash just to have more time around the Rosh Yeshiva, absorbing from him everything possible. (See Brachos 47b for the importance of attending to Torah giants.)