Sforno on Numbers 13:2/ספורנו על במדבר י״ג:ב׳

1שלח לך אנשים, do not allow the selection of these men to be made by the people themselves! We know from Deuteronomy 1,22 that the initiative of sending out spies came from the people and that Moses was put under pressure to do this. G’d was cautioning Moses that by allowing the people to select the spies themselves, that if they chose unsuitable candidates and they came back with a faulty report, the people would blame G’d for what was wrong with the country instead of the inadequate ability of the spies to correctly evaluate what they had seen. Once the blame would be laid at G’d’s doorstep it would be impossible to do teshuvah. In the event, the people did teshuvah when they said “we have sinned against You,” as reported in Deuteronomy 1,41 As far as the spies whom Moses sent out were concerned, while it is true that they were guilty in bringing about the refusal of the people to undertake the campaign to conquer the land, and all this was due to a lack of faith in G’d, they did report truthfully on the excellence of the land and they brought back with them proof of it. (compare verse 27) where they are quoted as having said that not only was the land good, but it was a land flowing with milk and honey; In Deuteronomy 1,25 Moses also agrees that they had reported on the excellence of the land. Their fault lay in their asserting that the country could not be conquered by the Jewish people. Once the people realised that the problem had been their own lack of faith and not any shortcoming they had ascribed to G’d, the way was paved for repentance to become acceptable. They immediately reversed themselves, offering to ascend and to participate in the conquest of the land. (compare verse 41 in our chapter) They prayed and cried to G’d regarding their sin, but G’d did not accept their prayer. Their sin had consisted of a desecration of the Lord’s name in public, something that cannot be atoned for except after the death of the guilty party. G’d had already alluded to this in Exodus 32,34 in connection with the sin of the golden calf when He had said וביום פקדי ופקדתי, “on the day when I mete out justice (literally “remember” i.e. review the deceased deeds, etc.) I will also judge, etc.” In other words, this atonement is reserved for people only posthumously.