Or HaChaim on Numbers 27:22/אור החיים על במדבר כ״ז:כ״ב

1 ויעש משה כאשר צוה ה׳ אותו, Moses did as G'd had instructed him, etc. The reason the Torah mentions something so obvious as Moses complying with G'd's instructions, is only to tell us that he did so promptly after having been so instructed. It also means that had Moses not specifically requested that G'd appoint a suitable leader now, G'd would not yet have given such instructions. Seeing that Moses' death was not that near at hand, and that there was no immediate need to appoint Joshua, Moses' conduct was a credit to him.