Why were they commanded to enter the city?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It was because of sins they had committed. They were told: "Enter the town" and "Enter the gate in prostration; We will forgive your sins". [Wahb]
2. They became tired of eating manna and quails (al-mann wa al-salwā), so they were told: "Go down to a town". The first town they encountered was Jericho (Arīḥā), and they were commanded to enter it.