As in Deuteronomy 2:24, so here again Moses recalls the Lord's command to go and possess the land of the Amorites. God, as the one who has begun to give Sihon and his land
to Israel, was preparing the way for them. Therefore, they in obedience could begin to tae possession
of the land.
31 And the LORD said to me, ‘Behold, I have begun to give Sihon and his land over to you. Begin to take possession, that you may occupy his land.’