 Rashi explained that even though God had not commanded Moses to call to Sihon in peace, Moses learned to do so from what God did when God first was about to give the Torah to Israel.God first took the Torah to Esau and Ishmael, although it was clear to God that they would not accept it, because God wished to begin with them in peace.Nachmanides disagreed, concluding that Moses sent messengers to Sihon before God instructed Moses to go to war with Sihon.