ויהי כאשר תמו כל אנשי המלחמה למות ...וידבר ה' אלי לאמור, "It was after all the arms-bearing men had finished dying, the Lord spoke to me, etc.⁠" According to the plain meaning of text Moses is telling the people that as soon as the Israelites had become aware that all the men who had been 20 years old at the Exodus had died, God communicated once more with Moses and commanded the people to march past the territory of Moav.
According to our sages in Taanit 30 God had not spoken (individually) with Moses since the time the spies had died and the generation of the adults who had been redeemed from Egypt had been condemned to die in the desert. This proved that Moses' elevated position was entirely due to the people he represented. When these people were in disgrace, Moses was made to feel this. This condition remained static for 38 years until the 15th of Av of the fortieth year. This day became a day of great rejoicing as the fact that God commenced His dialogue with Moses indicated that the people were once again in a state of grace. It was also a special day for Moses personally as it signaled the return of his prophetic powers. The reason that the prophetic powers did not already return to Moses on the 10th of Av, i.e. precisely after the anniversary of the debacle with the spies, was because at that time, in the second year when the decree against the people had been promulgated, Moses observed 7 days of mourning for the decree, a period when he would not have been the recipient of prophetic insights, seeing that a state of joy is required for a person to possess such powers. Now, on the 15th of the month of Av, both Moses and the people could rejoice simultaneously.
If you will peruse the text of the Torah starting with the debacle of the spies' mission, you will not find that God addressed Moses, i.e. the words וידבר ה' אל משה. You will only find ויאמר ה' אל משה, i.e. a level of communication reserved for prophets of lesser stature, people who receive an "indistinct message,⁠" the kind God referred to when He rebuked Miriam and Aaron in Numbers 12,6 (compare Baba Batra 121). This will also help you understand Jeremiah 1,6 who had said to God: "here I am only a lad, and I do not know how to speak, דבר.⁠" He did not mean that he had a speech impediment, but that due to his low level of prophetic insight he could not communicate his message with the appropriate degree of clarity. He alluded to this by adding the word אהה before saying א-ד-נ-י אלוהים, The fact that God communicated with Jeremiah on the lower level of prophecy is confirmed by verse 7 in that chapter, i.e. ויאמר ה' אלי. [Incidentally, seeing that in Korach, etc. we do find the formula of וידבר ה' אל משה, this may be proof that the uprising of Korach had occurred prior to the debacle with the spies. This editor has always felt that Korach's bid for power made little sense seeing that all the people who joined him were bound to perish in the desert, ignominiously, so why risk your life for such positions? Ed.].