ואת יהושוע צויתי, "And I commanded Joshua, etc.⁠" Moses meant that he commanded Joshua not to be afraid of these nations, as we find at the end of verse 22: לא תיראום "you must not be afraid of them.⁠" Moses did not repeat the words "your eyes are seeing" at the end of verse 22, as this is not something which forms the subject of a command.

The reason Moses preferred to record these instructions here instead of after the conquest of the lands of Sichon and Og and the settlement of the tribes of Reuven and Gad in those lands, is because the conditions which were attached to the settlement of these lands by these tribes, etc. This could have created the impression that Joshua required the assistance of the heroic men of those tribes before he would undertake the mission of conquering the land of Canaan. Seeing that it was God who would conduct the actual battles, Moses did not want a false impression to be created. He introduced the paragraph with the words ואת יהושוע, "and Joshua,⁠" to hint that Joshua's part was incidental, as suggested by the conjunctive letter ו. This is also why Moses concluded this paragraph with the words "for your God will fight on your behalf.⁠" Moses underlined the word הוא, "He Himself,⁠" to make it even less plausible for someone who had heard that the men of the tribes of Gad and Reuven had to cross the Jordan in full armour to conclude that this was an indication that the wars of conquest would be dangerous. I have already explained the purpose of that command in my commentary on Parshat Mattot. You may also wish to read my comments on the words את כל.

בעת ההיא לאמור, "at that time saying, etc.⁠" The time referred to is the time when Moses imposed his conditions on the tribes of Reuven and Gad. The word לאמור in this context may mean that Moses did not tell Joshua all this verbatim, but he told him words to this effect. I have shown that there are other instances when the word לאמור is employed in a similar fashion. It is also possible that the meaning is for Joshua to relay such a command to the Israelites at the time they would ready themselves to battle the seven Canaanite tribes, in order to remove fear from their hearts.

את כל אשר עשה, "all that He has done, etc.⁠" This statement incorporates the reason Moses insisted that the tribes of Reuven and Gad cross the river Jordan armed, ready to join the other tribes in the conquest of the West Bank. Moses says that God will do to the tribes on the West Bank what He had done to the Emorite Kings Sichon and Og. Just as God's help against those kings had been predicated on all of the tribes having readied themselves to do battle, so in order for God to do battle on behalf of the Israelites against the 31 kings on the West Bank, all the tribes had to be present in battle formation. In both instances it was God who did the actual fighting. In view of the above Moses was not able to say to Joshua "your own eyes have observed what God did to these two kings, etc.⁠" until after the two tribes had been commanded to cross the Jordan, etc. The collective merit of 12 tribes of Israel cannot be compared to the collective merit of 10 tribes. If God had been willing to fight on behalf of 12 tribes this was not proof that He would do the same on behalf of only 10 tribes. I have already explained this on Numbers 32,6.