‘ Also Yahweh was angry with me for your sakes, saying, “You also shall not go in there, Joshua the son of Nun, who stands before you, he shall go in there. Encourage you him, for he will cause Israel to inherit it.” '
But Moses own right to enter the land had also later been lost. He reminds them of what to him was a harsh fact. That he too now could not enter the land. And the reason that he could not enter the land was because he himself had sinned, partly as a result of Israel's disobedience. This disobedience is the connecting point with the previous verse. For in the end he too was forbidden entry into the land because of his later sin at Meribah (Numbers 20:12) when they were coming to Kadesh for the second time. That was due to the people's unbelief as well. And it was the possible unbelief of the people that he was speaking to now! Let them remember what their unbelief has done to him, and learn from it.
Such an abbreviated reference fits well with these being Moses' actual words to the actual people who had been the cause of his behaviour. He did not need to remind them of the circumstances. They remembered them all too well. No one who had been present in the camp would forget that dreadful day when the news spread around of God's judgment on Moses because he had got annoyed at their intransigence. With all their mutterings he was the one figure on whom they knew that they could always rely. And Moses knew that they would still feel guilty about it. But he wants them to recognise that his loss is Joshua's gain, so that they must faithfully support Joshua in order to demonstrate their sorrow at what they had done to him.
Up to that point at Meribah then (humanly speaking) it had been in God's mind that he should enter the land to possess it for Yahweh. But then he had lost that privilege. Now that privilege was to go to Joshua, the one who ‘stood before him', that is, was his second in command. That being so there had been no need to mention Joshua previously because all knew that he was destined to lead them into the land, and he, with Moses, would also have been responsible for giving the command to go forward in the previous situation. Thus he did not have to debate the question like Caleb did. He was firmly with Moses in his actions, and was the one who was to cause Israel to inherit (receive as a gift) the land. He does not want Joshua to be seen as having been just another scout. His appointment was from Yahweh.
Forgetting that this is a speech in which he is seeking to get over basic facts without worrying about the chronology causes some commentators difficulties. But Moses is simply bringing out salient facts. Their father's could not enter because of unbelief, he cannot enter because he had sinned when he was provoked. Both were excluded because of sin. Thus it is Joshua who will lead them forward. Joshua's official appointment was not until Numbers 27:18, although Moses was no doubt aware that he was grooming him for leadership right from his appointment of him as his ‘servant', and from his success against the Amalekites in Exodus 17. However this is a speech and he would not hesitate to put everything together without regard to time. It was the facts which mattered not when they happened. That is why he ignores Aaron. He is irrelevant to the point he is making.
(It is, of course, psychologically possible as some have suggested that Moses had a guilt feeling about his failure to persuade the unbelievers to go forward at that time, and dated his rejection back to that fact, but there is no other indication of it and it is not required as an explanation in a context like this).